Polynomial,Power, andRational Functions CHAPTER 2 2 text... · Polynomial,Power, andRational Functions 2.1 Linear and Quadratic ... For students:Aha! Insight,Martin Gardner.W.H.Freeman,1978.Available

2

Polynomial, Power,and Rational Functions

2.1 Linear and QuadraticFunctions and Modeling

2.2 Power Functions withModeling

2.3 Polynomial Functions of Higher Degree withModeling

2.4 Real Zeros of PolynomialFunctions

2.5 Complex Numbers

2.6 Complex Zeros and theFundamental Theorem ofAlgebra

2.7 Graphs of Rational Functions

2.8 Solving Equations in OneVariable

2.9 Solving Inequalities in OneVariable

C H A P T E R

umidity and relative humidity are measures used byweather forecasters. Humidity affects both our comfortand our health. If humidity is too low, our skin can

become dry and cracked, and viruses can live longer. If it is toohigh, it can make warm temperatures feel even warmer, andmold, fungi, and dust mites can live longer. Several questionsabout these topics are asked and answered on page XXX.

1

H

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 1

2 CHAPTER 2 Polynomial, Power, and Rational Functions

Chapter 2 OverviewChapter 1 laid a foundation of the general characteristics of functions, equa-tions, and graphs. In this chapter and the next two, we will explore the theoryand applications of specific families of functions. We begin this explorationby studying three interrelated families of functions: polynomial, power, andrational functions. These three families of functions are used in the social,behavioral, and natural sciences.

This chapter includes a thorough study of the theory of polynomial equations.We investigate algebraic methods for finding both real- and complex-numbersolutions of such equations and relate these methods to the graphical behav-ior of polynomial and rational functions. The chapter closes by extendingthese methods to inequalities in one variable.

Polynomial FunctionsPolynomial functions are among the most familiar of all functions.

Polynomial functions are defined and continuous on all real numbers. It isimportant to recognize whether a function is a polynomial function.

EXAMPLE 1 Identifying polynomial functionsWhich of the following are polynomial functions? For those that arepolynomial functions, state the degree and leading coefficient. For thosethat are not, explain why not.

(a) f �x� � 4x3 � 5x � �12

� (b) g �x� � 6x�4 � 7

(c) h�x� � �9�x�4�� 1�6�x�2� (d) k �x� � 15x � 2x4

SOLUTION (a) f is a polynomial function of degree 3 with leading coefficient 4.

(b) g is not a polynomial function because of the exponent �4.

What you’ll learn about■ Polynomial Functions■ Linear Functions and Their Graphs■ Average Rate of Change■ Linear Correlation and Modeling■ Quadratic Functions and

Their Graphs■ Free Fall

. . . and whyMany business and economicproblems can be modeled by linearfunctions. Quadratic and higherdegree polynomial functions can beused to model some manufacturingapplications.

2.1 LINEAR AND QUADRATIC FUNCTIONS AND MODELING

Definition Polynomial FunctionLet n be a nonnegative integer and let a0, a1, a2, . . . ,an � 1, an be realnumbers with an � 0. The function given by

f �x� � anxn � an � 1xn � 1 � · · ·� a2x2 � a1x � a0

is a . The is an.

The zero function f �x� � 0 is a polynomial function. It has no degreeand no leading coefficient.

leading coefficientpolynomial function of degree n

BIBLIOGRAPHYFor students: Aha! Insight, MartinGardner. W. H. Freeman, 1978. Availablethrough Dale Seymour Publications.The Imaginary Tale of the Story of i,Paul J. Nahin. Mathematical Associationof America, 1998.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 2

SECTION 2.1 Linear and Quadratic Functions and Modeling 3

(c) h is not a polynomial function because it cannot be simplified intopolynomial form. Notice that �9�x�4�� 1�6�x�2� � 3x2 � 4x.

(d) k is a polynomial function of degree 4 with leading coefficient�2.

The zero function and all constant functions are polynomial functions. Someother familiar functions are also polynomial functions, as shown below.

We study polynomial functions of degree higher than 2 in Section 2.3. For the remainder of this section, we turn our attention to the nature and uses of linear and quadratic polynomial functions.

Linear Functions and Their GraphsLinear equations and graphs of lines were reviewed in Sections P.3 and P.4,and many of the examples in Chapter 1 involved linear functions. We nowtake a closer look at the properties of linear functions.

A is a polynomial function of degree 1 and so has the form

f �x� � ax � b, where a and b are constants and a � 0.

If we use m for the leading coefficient instead of a and let y � f �x�, then thisequation becomes the familiar slope-intercept form of a line:

y � mx� b.

Vertical lines are not graphs of functions because they fail the vertical line test,and horizontal lines are graphs of constant functions. A line in the Cartesianplane is the graph of a linear function if and only if it is a , that is,neither horizontal nor vertical. We can apply the formulas and methods ofSection P.4 to problems involving linear functions.

EXAMPLE 2 Finding an equation of a linear functionWrite an equation for the linear function f such that f ��1� � 2 and f �3� � �2.

SOLUTIONSolve AlgebraicallyWe seek a line through the points ��1, 2� and �3, �2�. The slope is

m � �yx

2

2

�

�

yx

1

1� � �

�3�

�

2��

12�

� � ��

44� � �1.

slant line

linear function

Polynomial Functions of No and Low DegreeName Form Degree

Zero function f �x� � 0 Undefined

Constant function f �x� � a �a � 0� 0

Linear function f �x� � ax � b �a � 0� 1

Quadratic function f �x� � ax2 � bx � c �a � 0� 2

Now try Exercise 3.

BIBLIOGRAPHYFor teachers: Explorations in PrecalculusUsing the TI-82/TI-83, with AppendixNotes for TI-85, Cochener and Hodge.1997, Brooks/Cole Publishing Co., 1997.

Algebra Experiments II, ExploringNonlinear Functions, Ronald J. Carlsonand Mary Jean Winter. Addison-Wesley,1993. Available through Dale SeymourPublications.

Videos: Polynomials, ProjectMathematics!, California Institute ofTechnology. Available through DaleSeymour Publications.

Surprising Fact

Not all lines in the Cartesian plane aregraphs of linear functions.

OBJECTIVEStudents will be able to recognize andgraph linear and quadratic functions,and use these functions to model appli-cation problems.

MOTIVATEAsk students how they think the graphof y � (x � 2)2 � 5 is related to thegraph of y � x2. (Translated 2 units rightand 5 units up.)

LESSON GUIDEDay 1: Polynomial Functions; LinearFunctions and Their Graphs; AverageRate of ChangeDay 2: Linear Correlation; QuadraticFunctionsDay 3: Free Fall

ALERTSome students will attempt to calculateslopes using x in the numerator and y inthe denominator. Remind them that

slope � �rriusne

� � �cchh

aa

nn

gg

ee

iinn

xy

�.

REMARKNotice that the slope does not dependon the order of the points. We could use(x1, y1) � (3, �2) and (x2, y2) � (�1, 2).

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 3


Using this slope and the coordinates of ��1, 2� with the point-slope formula,we have

y � y1 � m�x � x1�

y � 2 � �1�x � ��1��

y � 2 � �x � 1

y � �x � 1

Converting to function notation gives us the desired form:

f �x� � �x � 1.

Support GraphicallyWe can graph y � �x � 1 and see that it includes the points ��1, 2� and�3, �2�. (See Figure 2.1.)

Confirm NumericallyUsingf �x� � �x � 1 we prove that f ��1� � 2 and f �3� � �2:

f ��1� � ��1� � 1 � 1 � 1 � 2 andf �3� � ��3� � 1 � �3 � 1 � �2.

Average Rate of ChangeAnother property that characterizes a linear function is its rate of change. The

of a function y � f �x� between x � a and x � b,a � b, is

�f �b

b� �

�

fa�a�

�.

The following relationship can be proved using calculus.

Because the average rate of change of a linear function is constant, it is calledsimply the of the linear function. The slope m in the formulaf �x� � mx� b is the rate of change of the linear function. In Exploration 1,we revisit Example 7 of Section P.4 in light of the rate of change concept.

rate of change

Constant Rate of ChangeA function defined on all real numbers is a linear function if and only ifit has a constant nonzero average rate of change between any two pointson its graph.

average rate of change

Now try Exercise 7.

Figure 2.1 The graph of y � �x � 1passes through (�1, 2) and (3, �2).(Example 2)

321

–1–2–3

y

x–5 –4 –3 –2 –1 321 4 5

(–1, 2)

(3, –2)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 4

The rate of change of a linear function is the signed ratio of the correspond-ing line’s rise over run. That is, for a linear function f �x� � mx� b,

rate of change � m � �rriusne

� � �cchhaannggee

iinn

yx

� � ��

�

yx

�.

This formula allows us to interpret the slope, or rate of change, of a linearfunction numerically. For instance, in Exploration 1 the value of the apartmentbuilding fell from $50,000 to $0 over a 25-yr period. In Table 2.1 we compute�y��x for the apartment building’s value (in dollars) as a function of time (inyears). Because the average rate of change �y��x is the nonzero con-stant�2000, the building’s value is a linear function of time decreasing at arate of $2000/yr.

In Exploration 1, as in other applications of linear functions, the constant termrepresents the value of the function for an input of 0. In general, for anyfunction f, f �0� is the . So for a linear function f �x� � mx� b,the constant term b is the initial value. For any polynomial function f �x� � anxn � · · ·� a1x � a0, the f �0� � a0 is its initialvalue. Finally, the initial value of any function—polynomial or otherwise—isthe y-intercept of its graph.

constant term

initial value of f

Table 2.1 Rate of Change of the Value of the Apartment

Building in Exploration 1: y � �2000x � 50,000

x (time) y (value) �x �y �y��x

0 50,000

1 �2000 �2000

1 48,000

1 �2000 �2000

2 46,000

1 �2000 �2000

3 44,000

1 �2000 �2000

4 42,000


TEACHER’S NOTEIt is important for students to see thatslope (from previous courses) becomesthe rate of change (in calculus), whichwe now foreshadow.

Modeling Depreciation with a Linear FunctionCamelot Apartments bought a $50,000 building and for tax purposesare depreciating it $2000 per year over a 25-yr period using straight-line depreciation.

1. What is the rate of change of the value of the building?

2. Write an equation for the value v�t� of the building as a linearfunction of the time t since the building was placed in service.

3. Evaluate v�0� and v�16�. 50,000; 18,000

4. Solve v�t� � 39,000. t � 5.5

EXPLORATION 1

EXPLORATION EXTENSIONSWhat would be different if the buildingsare depreciating $2500 per year over a20-year period?

Rate and Ratio

All rates are ratios, whether expressed asmiles per hour, dollars per year, or evenrise over run.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 5


We now summarize what we have learned about linear functions.

Linear Correlation and ModelingIn Section 1.6 we approached modeling from several points of view. Alongthe way we learned how to use a grapher to create a scatter plot, compute aregression line for a data set, and overlay a regression line on a scatter plot.We touched on the notion of correlation coefficient. We now go deeper intothese modeling and regression concepts.

Figure 2.2 shows five types of scatter plots. When the points of a scatter plotare clustered along a line, we say there is a between thequantities represented by the data. When an oval is drawn around the pointsin the scatter plot, generally speaking, the narrower the oval, the stronger thelinear correlation.

When the oval tilts like a line with positive slope (as in Figure 2.2a and b), thedata have a . On the other hand, when it tilts likea line with negative slope (as in Figure 2.2d and e), the data have a

. Some scatter plots exhibit little or no linearcorrelation (as in Figure 2.2c), or have nonlinear patterns.

A number that measures the strength and direction of the linear correlation ofa data set is the .

Correlation informs the modeling process by giving us a measure of goodnessof fit. Good modeling practice, however, demands that we have a theoreticalreason for selecting a model. In business, for example, fixed cost is modeledby a constant function. (Otherwise, the cost would not be fixed.)

Properties of the Correlation Coefficient, r1. �1 � r � 1.

2. When r 0, there is a positive linear correlation.

3. When r 0, there is a negative linear correlation.

4. When �r� � 1, there is a strong linear correlation.

5. When r � 0, there is weak or no linear correlation.

(linear) correlation coefficient, r

negative linear correlation

positive linear correlation

linear correlation

Characterizing the Nature of a Linear FunctionPoint of View Characterization

Verbal polynomial of degree 1

Algebraic f �x� � mx� b �m � 0�

Graphical slant line with slope m and y-intercept b

Analytical function with constant nonzero rate of change m:f is increasing if m 0, decreasing if m 0;initial value of the function� f �0� � b

ALERTSome students will attempt todetermine whether the correlation isstrong or weak by calculating a slope.Point out that these terms refer to howwell a line can model the data, not tothe slope of the line.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 6


In economics, a linear model is often used for the demand for a product as afunction of its price. For instance, suppose Twin Pixie, a large supermarketchain, conducts a market analysis on its store brand of doughnut-shaped oatbreakfast cereal. The chain sets various prices for its 15-oz box at its differentstores over a period of time. Then, using this data, the Twin Pixie researchersproject the weekly sales at the entire chain of stores for each price and obtainthe data shown in Table 2.2.

Table 2.2 Weekly Sales Data Based

on Marketing Research

Price per box Boxes sold

$2.40 38,320$2.60 33,710$2.80 28,280$3.00 26,550$3.20 25,530$3.40 22,170$3.60 18,260

Figure 2.2 Five scatter plots and the types of linear correlation they suggest.

y

x10 20 30 40 50

50

40

30

20

10

Strong positive linearcorrelation

(a)

y

x10 20 30 40 50

50

40

30

20

10

y

x10 20 30 40 50

50

40

30

20

10

Weak positive linearcorrelation

Little or no linearcorrelation

(b) (c)

y

x10 20 30 40 50

50

40

30

20

10

Strong negative linearcorrelation

(d)

y

x10 20 30 40 50

50

40

30

20

10

Weak negative linearcorrelation

(e)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 7


EXAMPLE 3 Modeling and predicting demandUse the data in Table 2.2 to write a linear model for demand (in boxes soldper week) as a function of the price per box (in dollars). Describe the strengthand direction of the linear correlation. Then use the model to predict weeklycereal sales if the price is dropped to $2.00 or raised to $4.00 per box.

SOLUTIONModelWe enter the data and obtain the scatter plot shown in Figure 2.3a. It appearsthat the data have a strong negative correlation.

We then find the linear regression model to be approximately

y � �15,358.93x � 73,622.50,

where x is the price per box of cereal and y the number of boxes sold.

Figure 2.3b shows the scatter plot for Table 2.2 together with a graph of theregression line. You can see that the line fits the data fairly well. The corre-lation coefficient of r � �0.98 supports this visual evidence.

Solve GraphicallyOur goal is to predict the weekly sales for prices of $2.00 and $4.00 per box.Using the value feature of the grapher, as shown in Figure 2.3c, we see thaty is about 42,900 when x is 2. In a similar manner we could find thaty � 12,190 when x is 4.

InterpretIf Twin Pixie drops the price for its store brand of doughnut-shaped oatbreakfast cereal to $2.00 per box, sales will rise to about 42,900 boxes perweek. On the other hand, if they raise the price to $4.00 per box, sales willdrop to around 12,190 boxes per week.

We summarize for future reference the analysis used in Example 3.

Quadratic Functions and Their GraphsA is a polynomial function of degree 2. Recall fromSection 1.3 that the graph of the squaring function f �x� � x2 is a parabola. Wewill see that the graph of every quadratic function is an upward or downwardopening parabola. This is because the graph of any quadratic function can beobtained from the graph of the squaring functionf �x� � x2 by a sequence oftranslations, reflections, stretches, and shrinks.

quadratic function

Regression Analysis1. Enter and plot the data (scatter plot).

2. Find the regression model that fits the problem situation.

3. Superimpose the graph of the regression model on the scatter plot,and observe the fit.

4. Use the regression model to make the predictions called for in theproblem.

Now try Exercise 49.

Figure 2.3 Scatter plot and regressionline graphs for Example 3.

[0, 5] by [–10000, 80000]

(c)

X=2 Y=42904.643

[2, 4] by [10000, 40000]

(b)

[2, 4] by [10 000, 40 000]

(a)

ALERTSome graphers display a linear regres-sion equation using a and b, where y � a � bx instead of y � ax � b.Caution students to be certain that theyunderstand the convention used by theparticular grapher they are using.

TEACHER’S NOTEOn some grapher, you need to selectDiagnostic On from the Catalog to seethe correlation coefficient.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 8


EXAMPLE 4 Transforming the squaring functionDescribe how to transform the graph of f �x� � x2 into the graph of the givenfunction. Sketch its graph by hand.

(a) g�x� � �(1/2)x2 � 3 (b) h�x� � 3�x � 2�2 � 1

SOLUTION(a) The graph of g�x� � ��1�2�x2 � 3 is obtained by vertically shrinking thegraph of f �x� � x2 by a factor of 1�2, reflecting the resulting graph acrossthe x-axis, and translating the reflected graph up 3 units. See Figure 2.4a.

(b) The graph of h�x� � 3�x � 2�2 � 1 is obtained by vertically stretchingthe graph of f �x� � x2 by a factor of 3 and translating the resulting graphleft 2 units and down 1 unit. See Figure 2.4b

The graph of f �x� � ax2, a 0, is an upward-opening parabola. When a 0,its graph is a downward-opening parabola. Regardless of the sign of a, the y-axisis the line of symmetry for the graph off �x� � ax2. The line of symmetry for aparabola is its , or for short. The point on the parabolathat intersects its axis is the of the parabola. Because the graph of a quadratic function is always an upward- or downward-opening parabola, its vertex is always the lowest or highest point of the parabola. The vertex off �x� � ax2 is always the origin, as seen in Figure 2.5.

Figure 2.5 The graph f (x) � ax2 for (a) a 0 and (b) a 0.

Expanding f �x� � a �x � h�2 � k and comparing the resulting coefficientswith the ax2 � bx � c, where the powers of x arearranged in descending order, we can obtain formulas for h and k.

f �x� � a�x � h�2 � k

� a�x2 � 2hx � h2� � k Expand (x � h)3.

� ax2 � ��2ah�x � �ah2 � k� Distributive property

� ax2 � bx � c Let b � �2ah and c � ah2 � k.

standard quadratic form

vertex

axis

(b)

f(x) = ax2, a < 0

vertex

axis

(a)

f(x) = ax2, a > 0

vertexaxisaxis of symmetry


Figure 2.4 The graph of f (x) � x2 (blue)shown with (a) g(x) � �(1/2)x2 � 3 and(b) h(x) � 3(x � 2)2 � 1. (Example 4)

y

(b)

5

–5

–5x

5

y

(a)

5

–5

–5x

5

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 9

Because b � �2ah and c � ah2 � k in the last line above,h � �b��2a� and k � c � ah2. Using these formulas, any quadratic function f �x� � ax2 � bx� ccan be rewritten in the form

f �x� � a�x � h�2 � k.

This for a quadratic function makes it easy to identify the vertexand axis of the graph of the function, and to sketch the graph.

The formula h � �b��2a� is useful for locating the vertex and axis of theparabola associated with a quadratic function. To help you remember it,notice that �b��2a� is part of the quadratic formula

x ��b � �

2b�a

2�� 4�a�c��.

(Cover the radical term.� You need not remember k � c � ah2 because youcan use k � f �h� instead.

EXAMPLE 5 Finding the vertex and axis of a quadraticfunction

Use the vertex form of a quadratic function to find the vertex and axis of thegraph off �x� � 6x � 3x2 � 5. Rewrite the equation in vertex form.

SOLUTIONSolve AlgebraicallyThe standard polynomial form of f is

f �x� � �3x2 � 6x � 5.

So a � �3, b � 6, and c � �5, and the coordinates of the vertex are

h � ��2ba� � ��

2(�6

3)� � 1 and

k � f �h� � f �1� � �3�1�2 � 6�1� � 5 � �2.

The equation of the axis is x � 1, the vertex is �1,�2�, and the vertex formof f is

f �x� � �3�x � 1�2 � ��2�.Now try Exercise 31.

Vertex Form of a Quadratic FunctionAny quadratic functionf �x� � ax2 � bx � c, a � 0, can be written inthe vertex form

f �x� � a�x � h�2 � k.

The graph off is a parabola with vertex �h, k� and axis x � h, whereh � �b��2a� and k � c � ah2. If a 0, the parabola opens upward, andif a 0, it opens downward. (See Figure 2.6.)

vertex form


Figure 2.6 The vertex is at x � �b�(2a),which therefore also describes the axis ofsymmetry. (a) When a 0, the parabolaopens upward. (b) When a 0, theparabola opens downward.

y

x

y = ax2 + bx + c

, a < 0x = – b2a

(b)

y

x

y = ax2 + bx + c

, a > 0x = – b2a

(a)

TEACHER’S NOTEAnother way of converting a quadraticfunction from the polynomial form f (x) � ax2 � bx � c to the vertex formf (x) � a(x � h)2 � k is completing thesquare, a method used in Section P.5 tosolve quadratic equations. Example 6illustrates this method.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 10

EXAMPLE 6 Using algebra to describe the graphof a quadratic function

Use completing the square to describe the graph of f �x� � 3x2 � 12x � 11.Support your answer graphically.

SOLUTIONSolve Algebraicallyf �x� � 3x2 � 12x � 11

� 3�x2 � 4x� � 11 Factor 3 from the x terms.

� 3�x2 � 4x � � � � � �� 11 Prepare to complete the square.

� 3�x2 � 4x � �22� � �22�� 11 Complete the square.

� 3�x2 � 4x � 4� � 3�4� � 11 Distribute the 3.

� 3�x � 2�2 � 1

The graph off is an upward-opening parabola with vertex ��2, �1�, axis ofsymmetry x � �2, and intersects the x-axis at about �2.577 and �1.423.The exact values of the x-intercepts are x � �2 � �3��3.

Support GraphicallyThe graph in Figure 2.7 supports these results.

We now summarize what we know about quadratic functions.

In economics, when demand is linear, revenue is quadratic. Example 7illustrates this by extending the Twin Pixie model of Example 3.

EXAMPLE 7 Predicting maximum revenueUse the model y � �15,358.93x � 73,622.50 from Example 3 to developa model for the total weekly revenue on doughnut-shaped oat breakfastcereal sales. Determine the maximum revenue and how to achieve it.

Characterizing the Nature of a Quadratic FunctionPoint of View Characterization

Verbal polynomial of degree 2

Algebraic f �x� � ax2 � bx � c or f �x� � a�x � h�2 � k �a � 0�

Graphical parabola with vertex �h, k� and axis x � h;opens upward if a 0, opens downward if a 0;initial value � y-intercept� f �0� � c;

x-intercepts� ��b � �

2b�a

2�� 4�a�c��



Figure 2.7 The graphs of f (x) � 3x2 �

12x � 11 and y � (x � 2)2 � 1 appear to beidentical. The vertex (�2, �1) is highlighted.(Example 6)

[–4.7, 4.7] by [–3.1, 3.1]

X=–2 Y=–1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 11

SOLUTIONModelRevenue can be found by multiplying the price per box,x, by the number ofboxes sold,y. So the total revenue is given by

R�x� � x • y � �15,358.93x2 � 73,622.50x,

a quadratic model.

Solve GraphicallyIn Figure 2.8, we find a maximum of about 88,227 occurs when x is about 2.40.

InterpretTo maximize revenue, Twin Pixie should set the price for its store brand ofdoughnut-shaped oat breakfast cereal at $2.40 per box. Based on the model,this will yield a total revenue of about $88,227.

Recall that the average rate of change of a linear function is constant. InExercise 77 you will see that the average rate of change of a quadratic func-tion is not constant.

In calculus you will study not only average rate of change but also instanta-neous rate of change. Such instantaneous rates include velocity and acceler-ation, which we now begin to investigate.

Free FallSince the time of Galileo Galilei (1564–1642) and Isaac Newton (1642–1727),the vertical motion of a body in free fall has been well understood. The verti-cal velocityand vertical position (height) of a free-falling body (as functions oftime) are classical applications of linear and quadratic functions.

These formulas disregard air resistance, and the two values given for g arevalid at sea level. We apply these formulas in Examples 8 and 9, and will usethem from time to time throughout the rest of the textbook.

EXAMPLE 8 Investigating free-fall motionAs a promotion for the Houston Astros downtown ballpark, a competition isheld to see who can throw a baseball the highest from the front row of the upperdeck of seats, 83 ft above field level. The winner throws the ball with an initialvertical velocity of 92 ft/sec and it lands on the infield grass. Find



TEACHER’S NOTEEmphasize that this free-fall model onlyapplies when the ball is thrown vertically.

Vertical Free-Fall MotionThe sand v of an object in free fall are given by

s�t� � � �12

� gt2 � v0t � s0 and v� t� � �gt � v0,

where t is time (in seconds),g � 32 ft/sec2 � 9.8 m/sec2 is the, v0 is the initial vertical velocityof the

object, and s0 is its initial height.acceleration due to gravity

vertical velocityheight

Figure 2.8 The revenue model forExample 7.

[0, 5] by [–10000, 100000]

X=2.3967298 Y=88226.727Maximum

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 12

(a) the maximum height of the baseball,

(b) its time in the air, and

(c) its vertical velocity when it hits the ground.

SOLUTIONModelBecause the distance units are in feet, we use g � 32 ft/sec2. It is given thats0 � 83 ft and v0 � 92 ft/sec. So the models are

s�t� � �16t2 � 92t � 83 and v�t� � �32t � 92.

(a) Solve AlgebraicallyThe maximum height is the maximum value of the quadratic function s.This maximum will occur at the vertex, which has coordinates

h � ��2ba� � ��

2(�92

16)� � 2.875 and

k � s�2.875� � �16�2.875�2 � 92�2.875� � 83 � 215.25.

InterpretThe maximum height of the baseball is about 215 ft above field level.

(b) Solve GraphicallyIn Figure 2.9, we plot height versus time and calculate the positive-valuedzero of the height function, which is t � 6.54.

Confirm AlgebraicallyUsing the quadratic formula, we obtain

t � ��92 �

�

�32

13,776�� 0.79 or 6.54.

InterpretThe baseball spends about 6.54 sec in the air.

(c) Solve NumericallyWe now turn to the linear model for vertical velocity.

v�6.54 . . .� � �32�6.54 . . .� � 92 � �117 ft/sec

InterpretThe baseball’s downward rate is about 117 ft/sec when it hits the ground.

Example 7 shows how the theory of free-fall motion can be used in practice.Though this theory was developed long before modern data collection devicesarrived upon the scene, devices such as the Calculator-Based RangerTM

(CBRTM) can help us appreciate this classical theory.

The data in Table 2.3 were collected on Monday, October 11, 1999, in Boone,North Carolina (about 1 km above sea level), using a CBR™ and a 15-cm


�92 � ��9�2��2� �� 4��1�6��8�3��

2��16�


Figure 2.9 The graph of y � �16x2 � 92x � 83 where y representsthe height of the baseball in feet andx represents time in seconds. (Example 7)

[0, 7] by [–50, 250]

X=6.5428502 Y=0Zero

Rounding Answers

Remember to carry all decimals in yourcalculations until you reach a final answer.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 13

rubber air-filled ball. The CBR™ was placed on the floor face up. The ballwas thrown upward above the CBR™, and it landed directly on the face ofthe device.

EXAMPLE 9 Modeling vertical free-fall motionUse the data in Table 2.3 to write models for the height and verticalvelocity of the rubber ball. Then use these models to predict the maxi-mum height of the ball and its vertical velocity when it hits the face ofthe CBR™.

SOLUTIONModel

First we make a scatter plot of the data, as shown in Figure 2.10a. Usingquadratic regression, we find the model for the height of the ball to be about

s�t� � �4.676t2 � 3.758t � 1.045,

with R2 � 0.999, indicating an excellent fit.

Our free-fall theory says the leading coefficient of �4.676 is �g�2, givingus a value for g � 9.352 m/sec2, which is a bit less than the theoretical valueof 9.8 m/sec2. We also obtain v0 � 3.758 m/sec. So the model for verticalvelocity becomes

v�t� � �gt � v0 � �9.352t � 3.758.

Solve Graphically and Numerically

The maximum height is the maximum value of s�t�, which occurs at thevertex of its graph. We can see from Figure 2.10b that the vertex hascoordinates of about �0.402, 1.800�.

In Figure 2.10c, to determine when the ball hits the face of the CBR™, wecalculate the positive-valued zero of the height function, which ist � 1.022. We turn to our linear model to compute the vertical velocity atimpact:

v�1.022� � �9.352�1.022� � 3.758� �5.80 m�sec.

Table 2.3 Rubber Ball Data from CBR™

Time (sec) Height (m)

0.0000 1.037540.1080 1.402050.2150 1.638060.3225 1.774120.4300 1.803920.5375 1.715220.6450 1.509420.7525 1.214100.8600 0.83173


ASSIGNMENT GUIDEDay 1: Ex. 1–12 oddsDay 2: Ex. 15–48, multiples of 3Day 3: Ex. 50, 51, 53–55, 63–66, 82, 83COOPERATIVE LEARNINGGroup Activity: Ex. 59, 60NOTES ON EXERCISESEx. 39–44 require the student toproduce a quadratic function withcertain qualities.Ex. 54, 56–63 offer some classicalapplications of quadratic functions.Ex. 64, 66, 67 are applications ofquadratic and linear regression.Ex. 70–75 provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 7, 21, 31, 33, 49, 55,61, 63Embedded Assessment: Ex. 40, 63

Reminder

Recall from Section 1.6 that R2 is thecoefficient of determination, whichmeasures goodness of fit.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 14

InterpretThe maximum height the ball achieved was about 1.80 m above the face of theCBR™. The ball’s downward rate is about 5.80 m/sec when it hits the CBR™.

The curve in Figure 2.10b appears to fit the data extremely well, and R2 � 0.999. You may have noticed, however, that Table 2.3 contains theordered pair �0.4300, 1.80392) and that 1.80392 1.800, which is the max-imum shown in Figure 2.10b. So, even though our model is theoreticallybased and an excellent fit to the data, it is not a perfect model. Despite itsimperfections, the model provides accurate and reliable predictions aboutthe CBR™ experiment. Now try Exercise 63.


FOLLOW-UPAsk the students to write a quadraticequation that is shifted 3 units to theleft and 4 units down from the origin.(f(x) � x2 � 6x � 5)

Figure 2.10 Scatter plot and graph of height versus time for Example 9.

[0, 1.2] by [–0.5, 2.0]

(c)

X=1.0222877 Y=0Zero

[0, 1.2] by [–0.5, 2.0]

(b)

X=.40183958 Y=1.8000558Maximum

[0, 1.2] by [–0.5, 2.0]

(a)

In Exercises 1–2, write an equation in slope-intercept form fora line with the given slope m and y-intercept b.

1. m � 8, b � 3.6 2. m � �1.8, b � �2

In Exercises 3–4, write an equation for the line containing thegiven points. Graph the line and points.

3. ��2, 4� and �3, 1� 4. �1, 5� and ��2, �3�

In Exercises 5–8, expand the expression.

5. �x � 3�2 x2 � 6x � 9 6. �x � 4�2 x2 � 8x � 16

7. 3�x � 6�2 3x2 � 36x � 108 8. �3�x � 7�2

In Exercises 9–10, factor the trinomial.

9. 2x2 � 4x � 2 2(x � 1)210. 3x2 � 12x � 12 3(x � 2)2

QUICK REVIEW 2.1 (For help, go to Sections A.2 and P.4.)

In Exercises 1–6, determine which are polynomial functions.For those that are, state the degree and leading coefficient.For those that are not, explain why not.

1. f �x� � 3x�5 � 17 2. f �x� � �9 � 2x

3. f �x� � 2x5 � �12

� x � 9 4. f �x� � 13

5. h�x� � �3

27x3 �� 8x6� 6. k�x� � 4x �5x2

In Exercises 7–12, write an equation for the linear functionfsatisfying the given conditions. Graph y � f �x�.

7. f ��5� � �1 and f �2� � 4

8. f ��3� � 5 and f �6� � �2

9. f ��4� � 6 and f ��1� � 2

10. f �1� � 2 and f �5� � 7

11. f �0� � 3 and f �3� � 0

12. f ��4� � 0 and f �0� � 2

SECTION 2.1 EXERCISES

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 15

In Exercises 13–18, match a graph to the function. Explain yourchoice.

13. f �x� � 2�x � 1�2 � 3 (a) 14. f �x� � 3�x � 2�2 � 7 (d)

15. f �x� � 4 � 3�x � 1�2 (b) 16. f �x� � 12 � 2�x � 1�2 (f)

17. f �x� � 2�x � 1�2 � 3 (e) 18. f �x� � 12 � 2�x � 1�2 (c)

In Exercises 19–22, describe how to transform the graph off �x� � x2 into the graph of the given function. Sketch each graphby hand.

19. g�x� ��x � 3�2 � 2 20. h�x� � �14

�x2 � 1

21. g�x� � �12

��x � 2�2 � 3 22. h�x� � �3x2 � 2

In Exercises 23–26, find the vertex and axis of the graph of thefunction.

23. f �x� � 3�x � 1�2 � 5 24. g�x� � �3�x � 2�2 � 1

25. f �x� � 5�x � 1�2 � 7 26. g�x� � 2�x � �3��2 � 4

In Exercises 27–32, find the vertex and axis of the graphof the function. Rewrite the equation for the function invertex form.

27. f �x� � 3x2 � 5x � 4 28. f �x� � �2x2 � 7x � 3

29. f �x� � 8x � x2 � 3 30. f �x� � 6 � 2x � 4x2

31. g�x� � 5x2 � 4 � 6x 32. h�x� � �2x2 � 7x � 4

In Exercises 33–38, use completing the square to describethe graph of each function. Support your answers graphically.

33. f �x� � x2 � 4x � 6 34. g�x� � x2 � 6x � 12

35. f �x� � 10 � 16x � x236. h�x� � 8 � 2x � x2

37. f �x� � 2x2 � 6x � 7 38. g�x� � 5x2 � 25x � 12

In Exercises 39–42, write an equation for the parabolashown, using the fact that one of the given points is the vertex.

39. 40.

41. 42.

In Exercises 43 and 44, write an equation for the quadratic function whose graph contains the given vertex and point.

43. Vertex �1, 3�, point �0, 5�44. Vertex ��2, �5�, point ��4, �27�

In Exercises 45–48, describe the strength and direction of thelinear correlation.

45. 46.

47. 48. y

x

50

40

30

20

10

10 20 30 40 50

y

x

50

40

30

20

10

10 20 30 40 50

y

x

50

40

30

20

10

10 20 30 40 50

y

x

50

40

30

20

10

10 20 30 40 50

[–5, 5] by [–15, 15]

(2, –13)

(–1, 5)

[–5, 5] by [–15, 15]

(4, –7)

(1, 11)

[–5, 5] by [–15, 15]

(2, –7)

(0, 5)

[–5, 5] by [–15, 15]

(–1, –3)

(1, 5)

(f)(e)

(d)(c)

(b)(a)


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 16

49. Comparing Age and Weight A group of male childrenwere weighed. Their ages and weights are recorded inTable 2.4.

(a) Draw a scatter plot of these data.

(b) Writing to Learn Describe the strength and direction ofthe correlation between age and weight.

50. Life Expectancy Table 2.5 shows the average number ofadditional years a U.S. citizen is expected to live forvarious ages.

(a) Draw a scatter plot of these data.

(b) Writing to Learn Describe the strength and directionof the correlation between age and life expectancy.

51. Straight-Line Depreciation Mai Lee bought a computerfor her home office and depreciated it over 5 years using thestraight-line method. If its initial value was $2350, what isits value 3 years later?$940

52. Costly Doll Making Patrick’s doll-making businesshas weekly fixed costs of $350. If the cost for materialsis $4.70 per doll and his total weekly costs average$500, about how many dolls does Patrick make eachweek? 32

53. Table 2.6 shows the average weekly earnings of constructionworkers for several years. Let x � 0 stand for 1970,x � 1for 1971, and so forth.

(a) Writing to Learn Find the linear regression model for thedata. What does the slope in the regression model represent?

(b) Use the linear regression model to predict the constructionworker average weekly earnings in the year 2005.

54. Finding Maximum Area Among all the rectangles whoseperimeters are 100 ft, find the dimensions of the one withmaximum area. 25 � 25 ft

55. Total Revenue The per unit price p (in dollars) of a populartoy when x units (in thousands) are produced is modeled bythe function

price� p � 12 � 0.025x.

The revenue (in thousands of dollars) is the product of theprice per unit and the number of units (in thousands)produced. That is,

revenue� xp � x�12 � 0.025x�.

(a) State the dimensions of a viewing window thatshows a graph of the revenue model for producing 0 to100,000 units.

(b) How many units should be produced if the total revenueis to be $1,000,000?

56. Finding the Dimensions of a Painting A large painting inthe style of Rubens is 3 ft longer than it is wide. If thewooden frame is 12 in. wide, the area of the picture andframe is 208 ft2, find the dimensions of the painting.

57. Using Algebra in Landscape Design Julie Stone designeda rectangular patio that is 25 ft by 40 ft. This patio issurrounded by a terraced strip of uniform width planted withsmall trees and shrubs. If the area A of this terraced strip is504 ft2, find the width x of the strip. 3.5 ft

Table 2.6 Construction Worker Average

Weekly Earnings

Year Weekly Earnings (dollars)

1970 1951980 3681990 5261995 5872000 702

Source: U.S. Bureau of Labor Statistics as reported in The NewYork Times Almanac, 2002.

Table 2.5 U.S. Life Expectancy

Age Life Expectancy(years) (years)

10 67.420 57.730 48.240 38.850 29.860 21.570 14.380 8.6

Source: U.S. National Center for Health Statistics, VitalStatistics of the United States.

Table 2.4 Children’s Age and Weight

Age (months) Weight (pounds)

18 2320 2524 2426 3227 3329 2934 3539 3942 44


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 17

58. Management Planning The Welcome Home apartmentrental company has 1600 units available, of which 800 are currently rented at $300 per month. A market survey indicatesthat each $5 decrease in monthly rent will result in 20 newleases.

(a) Determine a function R�x� that models the total rentalincome realized by Welcome Home, where x is the numberof $5 decreases in monthly rent.

(b) Find a graph of R�x� for rent levels between $175 and $300(that is, 0� x � 25) that clearly shows a maximum for R�x�.(c) What rent will yield Welcome Home the maximummonthly income? $250 per month

59. Group Activity Beverage Business The Sweet DripBeverage Co. sells cans of soda pop in machines. It findsthat sales average 26,000 cans per month when the cans sellfor 50¢ each. For each nickel increase in the price, the salesper month drop by 1000 cans.

(a) Determine a function R�x� that models the total revenuerealized by Sweet Drip, where x is the number of $0.05increases in the price of a can.

(b) Find a graph of R�x� that clearly shows a maximum forR�x�.(c) How much should Sweet Drip charge per can to realizethe maximum revenue? What is the maximum revenue?

60. Group Activity Sales Manager Planning Jack was namedDistrict Manager of the Month at the Sylvania Wire Co. dueto his hiring study. It shows that each of the 30 salespersons hesupervises average $50,000 in sales each month, and that foreach additional salesperson he would hire, the average saleswould decrease $1000 per month. Jack concluded his studyby suggesting a number of salespersons that he should hireto maximize sales. What was that number? 10

61. Baseball Throwing Machine The Sandusky Little Leagueuses a baseball throwing machine to help train 10-year-oldplayers to catch high pop-ups. It throws the baseball straightup with an initial velocity of 48 ft/sec from a height of3.5 ft.

(a) Find an equation that models the height of the ballt seconds after it is thrown. h � �16t2 � 48t � 3.5

(b) What is the maximum height the baseball will reach?How many seconds will it take to reach that height?

62. Fireworks Planning At the Bakersville Fourth of Julycelebration, fireworks are shot by remote control into theair from a pit that is 10 ft below the earth’s surface.

(a) Find an equation that models the height of an aerialbomb t seconds after it is shot upwards with an initialvelocity of 80 ft /sec. Graph the equation.

(b) What is the maximum height above ground level that theaerial bomb will reach? How many seconds will it take toreach that height? 90 ft, 2.5 sec

63. Landscape Engineering In her firstproject after being employed by LandScapes International, Becky designsa decorative water fountain that willshoot water to a maximum height of 48 ft. What should be the initial velo-city of each drop of water to achievethis maximum height? (Hint: Use a gra-pher and a guess-and-check strategy.)

64. Patent Applications Using quadratic regression on the datain Table 2.7, predict the year when the number of patentapplication will reach 350,000. Let x � 0 stand for 1980,x � 1 for 1981 and so forth. 2003

65. Highway Engineering Interstate 70 west of Denver,Colorado, has a section posted as a 6% grade. This means thatfor a horizontal change of 100 ft there is a 6-ft vertical change.

(a) Find the slope of this section of the highway. 0.06

(b) On a highway with a 6% grade what is the horizontaldistance required to climb 250 ft? � 4167 ft

(c) A sign along the highway says 6% grade for the next7 mi. Estimate how many feet of vertical change there arealong those 7 mi. (There are 5280 ft in 1 mile.)

6%GRADE

6% grade

Table 2.7 U.S. Patent Applications

Year Applications (thousands)

1980 113.01985 127.11990 176.71995 228.81996 211.61997 233.01998 261.41999 289.5

Source: U.S. Bureau of the Census, Statistical Abstract of theUnited States, 1998 (Washington, D.C., 2001).


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 18

66. A group of female children were weighed. Their ages andweights are recorded in Table 2.8.

(a) Draw a scatter plot of the data.

(b) Find the linear regression model. y � 0.68x � 9.01

(c) Interpret the slope of the linear regression equation.

(d) Superimpose the regression line on the scatter plot.

(e) Use the regression model to predict the weight of a30-month-old girl. � 29.41 lb

67. Table 2.9 gives the average salaries for NBA players overseveral seasons.

(a) Draw a scatter plot of the data. Let x be the number of years after1990 in which the season started.

(b) Find the linear regression model.

(c) Interpret the slope of the linearregression equation.

(d) Superimpose the regression line on the scatter plot.

(e) Use the regression model to predict the average salaryfor NBA players during the 2005–2006 season.

In Exercises 68–69, complete the analysis for the given BasicFunction.

68. Analyzing a Function

69. Analyzing a Function

Standardized Test Questions70. True or False The initial value of f �x� � 3x2 � 2x � 3 is 0.

Justify your answer.

71. True or False The graph of the function f �x� � x2 � x � 1has no x-intercepts. Justify your answer.

In Exercises 72–75, you may use a graphing calculator to solvethe problem.

In Exercises 72–73,f �x� � mx� b, f ��2� � 3, and f �4� � 1.

72. What is the value of m? (e)

(a) 3 (b) �3 (c) �1 (d) 1�3 (e) �1�3

73. What is the value of b? (c)

(a) 4 (b) 11�3 (c) 7�3 (d) 1 (e) �1�3

BASIC FUNCTIONS The Squaring Functionf �x� � x2

Domain:Range:Continuity:Increasing-decreasing behavior:Symmetry:Boundedness:Local extrema:Horizontal asymptotes:Vertical asymptotes:End behavior:

BASIC FUNCTIONS The Identity Functionf �x� � xDomain:Range:Continuity:Increasing-decreasing behavior:Symmetry:Boundedness:Local extrema:Horizontal asymptotes:Vertical asymptotes:End behavior:

Table 2.9 National Basketball Association

Average Player Salaries

Season Salary (millions)

1991–1992 1.11992–1993 1.31993–1994 1.51994–1995 1.81995–1996 2.01996–1997 2.31997–1998 2.61998–1999 3.01999–2000 3.62000–2001 4.22001–2002 4.5

Source: USA TODAY CAREERS NETWORK,http://www.usatoday.com/sports/nba/stories/2001-02-salaries-was.htm

Table 2.8 Children’s Ages and Weights

Age (months) Weight (pounds)

19 2221 2324 2527 2829 3131 2834 3238 3443 39


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 19

In Exercises 74–75, let f �x� � 2�x � 3�2 �5.

74. What is the axis of symmetry of the graph of f ? (b)

(a) x � 3 (b) x � �3 (c) y � 5 (d) y � �5 (e) y � 0

75. What is the vertex of f ? (e)

(a) �0,0� (b) �3,5� (c) �3,�5� (d) ��3,5� (e) ��3,�5�

Explorations76. Writing to Learn Identifying Graphs of Linear Functions

(a) Which of the lines graphed below are graphs of linearfunctions? Explain.

(b) Which of the lines graphed below are graphs of functions?Explain.

(c) Which of the lines graphed below are not graphs offunctions? Explain.

77. Average Rate of Change Let f �x� � x2, g�x� � 3x � 2,h�x� � 7x � 3, k�x� � mx� b, and l�x� � x3.

(a) Compute the average rate of change of f from x � 1 tox � 3. 4

(b) Compute the average rate of change of f from x � 2 tox � 5. 7

(c) Compute the average rate of change of f from x � a tox � c. c � a

(d) Compute the average rate of change of g from x � 1 tox � 3. 3

(e) Compute the average rate of change of g from x � 1 tox � 4. 3

(f) Compute the average rate of change of g from x � a tox � c. 3

(g) Compute the average rate of change of h from x � a tox � c. 7

(h) Compute the average rate of change ofk from x � a tox � c. m

(i) Compute the average rate of change of l from x � a tox � c. c2 � ac � a2

Extending the Ideas78. Minimizing Sums of Squares The linear regression line is

often called the because it minimizes thesum of the squares of the , the differencesbetween actual y values and predicted y values:

residual� yi � �axi � b�,

where �xi, yi� are the given datapairs and y � ax� b is theregression equation, as shownin the figure.

Use these definitions toexplain why the regressionline obtained from reversingthe ordered pairs in Table 2.2is not the inverse of the func-tion obtained in Example 3.

79. Median-Median Line Read about the median-median line bygoing to the Internet, your grapher owner’s manual, or a library.Then use the following data set to complete this problem.

��2, 8�, �3, 6�, �5, 9�, �6, 8�, �8, 11�, �10, 13�, �12, 14�, �15, 4�(a) Draw a scatter plot of the data.

(b) Find the linear regression equation and graph it.

(c) Find the median-median line equation and graph it.

(d) Writing to Learn For this data, which of the two linesappears to be the line of better fit? Why?

80. Suppose b2 � 4ac 0 for the equation ax2 � bx � c � 0.

(a) Prove that the sum of the two solutions of this equationis �b�a.

(b) Prove that the product of the two solutions of this equationis c�a.

81. Connecting Algebra and Geometry Prove that the axis ofthe graph of f �x� � �x � a��x � b� is x � �a � b��2, wherea and b are real numbers.

82. Connecting Algebra and Geometry Identify the vertex ofthe graph of f �x� � �x � a��x � b�, where a and b are anyreal numbers.

83. Connecting Algebra and Geometry Prove that if x1 and x2

are real numbers and are zeros of the quadratic functionf �x� � ax2 � bx � c, then the axis of the graph of f isx � �x1 � x2��2.

residualsleast-square lines

321

–1–2–3

y

x–5 –4 –3 –2 –1 321 4 5

(vi)

321

–1

–3

y

x–5 –4 –3 –2 –1 321 5

(v)

321

–1–2–3

y

x–5 –4 –3 –2 –1 321 4 5

(iv)

321

–3

y

x–5 –4 –3 –2 –1 321 4 5

(iii)

321

–1–2–3

y

x–5 –4 –3 –1 321 4 5

(ii)

32

–1–2–3

y

x–5 –4 –3 –2 –1 21 4 5

(i)


y

x10 20 30 40 50

50

40

30

20

10

(xi, yi)

yi � (axi � b)

y � ax � b

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 20

Power Functions and VariationFive of the basic functions introduced in Section 1.3 were power functions.Power functions are an important family of functions in their own right andare important building blocks for other functions.

In general, if y � f �x� varies as a constant power of x, then y is a power func-tion of x. Many of the most common formulas from geometry and science arepower functions.

Name Formula Power Constant of Variation

Circumference C � 2�r 1 2�

Area of a circle A � �r 2 2 �

Force of gravity F � k�d2 �2 k

Boyle’s Law V � k�P �1 k

These four power function models involve output-from-input relationshipsthat can be expressed in the language of variation and proportion:

• The circumference of a circle varies directly as its radius.

• The area enclosed by a circle is directly proportional to the square of its radius.

• The force of gravity acting on an object is inversely proportional to thesquare of the distance from the object to the center of the Earth.

• Boyle’s Law states that the volume of an enclosed gas (at a constanttemperature) varies inversely as the applied pressure.

The power function formulas with positive powers are statements ofand power function formulas with negative powers are

statements of . Unless the word inverselyis included in avariation statement, the variation is assumed to be direct, as in Example 1.

inverse variationdirect variation

SECTION 2.2 Power Functions with Modeling 21

What you’ll learn about■ Power Functions and Variation■ Graphs of Power Functions■ Modeling with Power Functions

. . . and whyPower functions specify theproportional relationships ofgeometry, chemistry, and physics.

2.2 POWER FUNCTIONS WITH MODELING

OBJECTIVEStudents will be able to sketch powerfunctions in the form of f (x) � k x a

(where k and a are rational numbers).

MOTIVATEAsk students to predict what the graphsof the following functions will look likewhen x 0, 0 x 1, and x 1:a) f (x) � x3

b) f (x) � �x�

LESSON GUIDEDay 1: Power functions; GraphsDay 2: Modeling

TEACHING NOTES1. To help students with the meaning of

directly and inversely proportional,have them calculate three or fourareas of circles with different radiiand note that as the radius increasesso does the area. Ask students whatwould hapen to the value of V inBoyle’s law if the value of P wereincreased. (As P increases in value,V decreases in value, therefore wesay it is inversely proportional.)

2. You may wish to have students graphone direct and one inverse variationin Quadrant I, either by hand or usinga grapher, to show that directvariations are increasing functions,and inverse variations are decreasingin Quadrant I.

Definition Power FunctionAny function that can be written in the form

f �x� � k • xa, where k and a are nonzero constants,

is a . The constant a is the , and k is the

, or . We say f �x� the ath

power of x, or f �x� the ath power of x.is proportional tovaries asconstant of proportionof variation

constantpowerpower function

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 21

EXAMPLE 1 Writing a power function formulaFrom empirical evidence and the laws of physics it has been found that theperiod of time T for the full swing of a pendulum varies as the square rootof the pendulum’s length l, provided that the swing is small relative to thelength of the pendulum. Express this relationship as a power function.

SOLUTION Because it does not state otherwise, the variation is direct. Sothe power is positive. The wording tells us that T is a function of l. Usingk as the constant of variation gives us

T�l� � k�l� � k • l1�2.

Section 1.3 introduced five basic power functions:

x, x2, x3, x�1 � �1x

�, and x1�2 � �x�.

Example 2 describes two other power functions: the cube root functionandthe inverse-squarefunction.

EXAMPLE 2 Analyzing power functionsState the power and constant of variation for the function, graph it, andanalyze it.

(a) f �x� � �3 x� (b) g�x� � �x12�

SOLUTION(a) Because f �x� � �3

x� � x1�3 � 1 • x1�3, its power is 1�3, and its constantof variation is 1. The graph of f is shown in Figure 2.11a.

Domain: All realsRange: All realsContinuousIncreasing for all xSymmetric with respect to the origin (an odd function)Not bounded above or belowNo local extremaNo asymptotesEnd behavior: lim

x→�∞�3 x� � �∞ and lim

x→∞�3 x� � ∞

Interesting fact: The cube root function f �x� � �3 x� is the inverse of thecubing function.

(b) Because g�x� � 1�x2 � x�2 � 1 • x�2, its power is �2, and its constantof variation is 1. The graph of g is shown in Figure 2.11b.

Domain:��∞, 0� � �0, ∞�Range:�0, ∞�Continuous on its domain; discontinuous at x � 0Increasing on ��∞,0�; decreasing on �0, ∞�Symmetric with respect to the y-axis (an even function)Bounded below, but not aboveNo local extrema



Figure 2.11 The graphs of (a) f (x) � �

3 x� � x1/3 and (b) g (x) � 1/x2 � x�2. (Example 2)

[–4.7, 4.7] by [–3.1, 3.1]

(b)

[–4.7, 4.7] by [–3.1, 3.1]

(a)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 22

EXPLORATION EXTENSIONSGraph f (x) � 2x, g(x) � 2x3, and h (x) � 2x5. How do these graphs differ from the graphs in Question 1? Do they have any ordered pairs in common? Now graph f (x) � �2x, g(x) � �2x3, and h(x) � �2x5.Compare these graphs with the graphsin the first part of the exploration.

Graphs of Power FunctionsA single-term polynomial function is a power function that is also called amonomial function.

So the zero function and constant functions are monomial functions, but the moretypical monomial function is a power function with a positive integer power,which is the degree of the monomial. The basic functions x, x2, and x3 are typi-cal monomial functions. It is important to understand the graphs of monomialfunctions because every polynomial function is a sum of monomial functions.

In Exploration 1 we take a close look at six basic monomial functions. Theyhave the form xn for n � 1, 2, . . . , 6. We group them by even and odd powers.

Horizontal asymptote:y � 0; vertical asymptote:x � 0End behavior: lim

x→�∞�1�x2� � 0 and lim

x→∞�1�x2� � 0

Interesting fact:g�x� � 1�x2 is the basis of scientific inverse-square laws, forexample, the inverse-square gravitational principle F � k�d2 mentioned above.

So g�x� � 1�x2 is sometimes called the inverse-square function, but it is notthe inverse of the squaring function but rather its multiplicativeinverse.



Comparing Graphs of Monomial FunctionsGraph the triplets of functions in the stated windows and explain howthe graphs are alike and how they are different. Consider the relevantaspects of analysis from Example 2. Which ordered pairs do all threegraphs have in common?

1. f �x� � x, g�x� � x3, and h�x� � x5 in the window �2.35, 2.35�by �1.5, 1.5�, then �5, 5� by �15, 15�, and finally �20, 20�by �200, 200�.

2. f �x� � x2, g�x� � x4, and h�x� � x6 in the window �1.5, 1.5� by�0.5, 1.5�, then �5, 5� by �5, 25�, and finally �15, 15� by�50, 400�.

EXPLORATION 1

Definition Monomial FunctionAny function that can be written as

f �x� � k or f �x� � k • xn,

where k is a constant and n is a positive integer, is a .monomial function

From Exploration 1 we see that

f �x� � xn is even if n is even and odd if n is odd.

Because of this symmetry, it is enough to know the first quadrant behavior off �x� � xn. Figure 2.12 shows the graphs of f �x� � xn for n � 1, 2, . . . , 6 inthe first quadrant near the origin.

Figure 2.12 The graphs of f (x) � xn,0 � x � 1, for n � 1, 2, . . . , 6.

[0, 1] by [0, 1]

(1, 1)

(0, 0)

x

x2

x3

x4

x5

x6

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 23

The following conclusions about the basic function f �x� � x3 can be drawnfrom your investigations in Exploration 1.

EXAMPLE 3 Graphing monomial functionsDescribe how to obtain the graph of the given function from the graph ofg�x� � xn with the same power n. Sketch the graph by hand and supportyour answer with a grapher.

(a) f �x� � 2x3 (b) f �x� � � �23

� x4

SOLUTION(a) We obtain the graph of f �x� � 2x3 by vertically stretching the graph ofg�x� � x3 by a factor of 2. Both are odd functions. See Figure 2.14a.

(b) We obtain the graph of f �x� � ��2�3�x4 by vertically shrinking the graphof g�x� � x4 by a factor of 2�3 and then reflecting it across the x-axis. Bothare even functions. See Figure 2.14b.

We ask you to explore the graphical behavior of power functions of the formx�n and x1�n, where n is a positive integer, in Exercise 65.



ALERTSome students may have troubleentering exponents on a grapher.Careful attention must be given to thesyntax and placement of parentheses.

Figure 2.14 The graphs of (a) f (x) � 2x3 with basic monomial g(x) � x3, and(b) f (x) � �(2/3)x 4 with basic monomial g(x) � x 4. (Example 3)

[–2, 2] by [–16, 16]

(b)

[–2, 2] by [–16, 16]

(a)

BASIC FUNCTIONS The Cubing Functionf �x� � x3

Domain: All realsRange: All realsContinuousIncreasing for all xSymmetric with respect to the origin (an odd function)Not bounded above or belowNo local extremaNo horizontal asymptotesNo vertical asymptotesEnd behavior: lim

x→�∞x3 � �∞ and lim

x→∞x3 � ∞Figure 2.13 The graph of f (x) � x3.

[–4.7, 4.7] by [–3.1, 3.1]

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 24

The graphs in Figure 2.15 represent the four general shapes that are possiblefor power functions of the form f �x� � kxa for x 0. In every case, the graphof f contains �1, 1�. Those with positive powers also pass through �0, 0�.Those with negative exponents are asymptotic to both axes.

When k 0, the graph lies in Quadrant I, but when k 0, the graph isin Quadrant IV. Notice that every power function passes through the point�1, k�.

In general, for any power function f �x� � k • xa, one of three following thingshappens when x 0.

• f is undefined for x 0, as is the case for f �x� � x1�2 and f �x� � x�.

• f is an even function, so f is symmetric about the y-axis, as is the case forf �x� � x�2 and f �x� � x2�3.

• f is an odd function, so f is symmetric about the origin, as is the case forf �x� �x�1 and f �x� � x7�3.

Predicting the general shape of the graph of a power function is a two-stepprocess as illustrated in Example 4.

EXAMPLE 4 Graphing power functions f (x) � k • xa

Observe the values of the constants k and a. Describe the portion of thecurve that lies in Quadrant I or IV. Determine whether f is even, odd, orundefined for x 0. Describe the rest of the curve if any. Graph thefunction to see whether it matches the description.

(a) f �x� � 2x�3 (b) f �x� � �0.4x1.5 (c) f �x� � �x0.4

SOLUTION(a) Because k � 2 is positive and a � �3 is negative, the graph passesthrough �1, 2� and is asymptotic to both axes. The graph is decreasing inthe first quadrant. The function f is odd because

f ��x� � 2��x��3 � ��

2x�3� � � �

x23� � �2x�3 � �f �x�.

So its graph is symmetric about the origin. The graph in Figure 2.16asupports all aspects of the description.

(b) Because k � �0.4 is negative and a � 1.5 1, the graph contains �0, 0� and passes through �1, �0.4�. In the fourth quadrant, it is decreasing.The function f is undefined for x 0 because

f �x� � �0.4x1.5 � ��25

� x3�2 � ��25

� ��x��3,

and the square-root function is undefined for x 0. So the graph of f has nopoints in Quadrants II or III. The graph in Figure 2.16b matches thedescription.


Figure 2.15 The graphs of f (x) � k • xa forx 0. (a) k 0, (b) k 0.

0

1 32

(b)

x

y

(1, k)

a < 0 a > 1 a = 1

0 < a < 1

0 1 32

(a)

x

y

(1, k)

a < 0 a > 1 a = 1

0 < a < 1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 25

(c) Because k � �1 is negative and 0 a 1, the graph contains �0, 0� andpasses through �1, �1�. In the fourth quadrant, it is decreasing. The functionf is even because

f ��x� � ��x�0.4 � ��x�2�5 � ��5��x��2 � ��5

x��2

� ��5x��2� �x0.4 � f �x�.

So the graph of f is symmetric about the y-axis. The graph in Figure 2.16cfits the description.

The following information about the basic function f �x� � �x� follows fromthe investigation in Exercise 65.



ALERT

Some graphing calculators will only produce the portion of the graph in Figure 2.14c for x 0. Be sure to check the domain of any function graphed with technology.

Figure 2.16 The graphs of (a) f (x) � 2x�3, (b) f (x) � �0.4x 1.5, and (c) f (x) � �x0.4. (Example 4)

[–4.7, 4.7] by [–3.1, 3.1]

(c)

[–4.7, 4.7] by [–3.1, 3.1]

(b)[–4.7, 4.7] by [–3.1, 3.1]

(a)

BASIC FUNCTIONS The Square Root Functionf �x� � �x�Domain:0,∞�Range:0,∞�Continuous on 0,∞�Increasing on 0,∞�No symmetryBounded below but not aboveLocal minimum at x � 0No horizontal asymptotesNo vertical asymptotesEnd behavior: lim

x→∞�x� � ∞Figure 2.17 The graph of f (x) � �x�.

[–4.7, 4.7] by [–3.1, 3.1]

Modeling with Power FunctionsNoted astronomer Johannes Kepler (1571–1630) developed three laws of plan-etary motion that are used to this day. Kepler’s Third Law states that the squareof the period of orbit T (the time required for one full revolution around theSun) for each planet is proportional to the cube of its average distance a from

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 26

the Sun. Table 2.10 gives the relevant data for the six planets that were knownin Kepler’s time. The distances are given in millions of kilometers, or gigame-ters (Gm).

EXAMPLE 5 Modeling planetary data with a powerfunction

Use the data in Table 2.10 to obtain a power function model for orbitalperiod as a function of average distance from the Sun. Then use the modelto predict the orbital period for Neptune, which is 4497 Gm from the Sunon average.

SOLUTIONModel

First we make a scatter plot of the data, as shown in Figure 2.18a. Usingpower regression, we find the model for the orbital period to be about

T �a� � 0.20a1.5 � 0.20a3�2 � 0.20 �a�3�.

Figure 2.18b shows the scatter plot for Table 2.10 together with a graphof the power regression model just found. You can see that the curvefits the data quite well. The coefficient of determination is R2 �0.999999912, indicating an amazingly close fit and supporting the visualevidence.

Solve Numerically

To predict the orbit period for Neptune we substitute its average distancefrom the Sun in the power regression model:

T�4497� � 0.2�4497�1.5 � 60,313.

Interpret

It takes Neptune about 60,313 days to orbit the Sun, or about 165 years,which is the value given in the National Geographic Atlas of the World.

Table 2.10 Average Distances and Orbit Periods for the

Six Innermost Planets

Planet Average Distance Period offrom Sun (Gm) Orbit (days)

Mercury 57.9 88Venus 108.2 225Earth 149.6 365.2Mars 227.9 687Jupiter 778.3 4332Saturn 1427 10,760

Source: Shupe, Dorr, Payne, Hunsiker, et al., National Geographic Atlas of the World(rev. 6th ed.). Washington, DC: National Geographic Society, 1992, plate 116.


A Bit of History

Example 5 shows the predicitive power of awell founded model. Exercise 67 asks you tofind Kepler’s elegant form of the equation,T2 � a3, which he reported in The Harmonyof the World in 1619.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 27

Figure 2.18c reports this result and gives some indication of the relativedistances involved. Neptune is much farther from the Sun than the six inner-most planets and especially the four closest to the Sun—Mercury, Venus,Earth, and Mars.

In Example 6, we return to free-fall motion, with a new twist. The data in thetable come from the same CBR™ experiment referenced in Example 9 ofSection 2.1. This time we are looking at the downward distance (in meters)the ball has traveled since reaching its peak height and its downward speed(in meters per second). It can be shown (see Exercise 68) that free-fall speedis proportional to a power of the distance traveled.

EXAMPLE 6 Modeling free-fall speed versus distanceUse the data in Table 2.11 to obtain a power function model for speed pversus distance traveled d. Then use the model to predict the speed of theball at impact given that impact occurs when d � 1.80 m.

SOLUTIONModel

Figure 2.19a is a scatter plot of the data. Using power regression, we findthe model for speed versus distance to be about

p�d� � 4.03d0.5 � 4.03d1�2 � 4.03�d�.

Table 2.11 Rubber Ball Data from

CBR™ Experiment

Distance (m) Speed (m/s)

0.00000 0.000000.04298 0.823720.16119 1.711630.35148 2.458600.59394 3.052090.89187 3.742001.25557 4.49558



ASSIGNMENT GUIDEDay 1: Ex. 3–48 multiples of 3Day 2: Ex. 51, 52, 55, 66, 68, 69COOPERATIVE LEARNINGGroup Activity: Ex. 64NOTES ON EXERCISESEx. 29–50 encourage students to thinkabout the appearance of functions with-out using a grapher.Ex. 51–54 are classical applications ofmonomial power functions.Ex. 55 and 57 are applications of regres-sion analysis.Ex. 58–63 provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 17, 37, 39, 41, 53, 55, 57Embedded Assessment: Ex. 45, 55, 66

FOLLOW-UPAsk . . .What would the graph of f (x) � �3x 1/2

look like? (Since 0 � 1� 2 � 1, the graph isin the first quadrant and undefined forx � 0; the coefficient �3 stretches thegraph and reflects it over the x-axis.)

Figure 2.18 Scatter plot and graphs for Example 5.

[0, 5000] by [–10000, 65000]

Y1=0.2X^1.5

X=4497 Y=60313.472[–100, 1500] by [–1000, 12000]

(b)

[–100, 1500] by [–1000, 12000]

(a)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 28

(See margin notes.) Figure 2.19b shows the scatter plot for Table 2.11together with a graph of the power regression equation just found. You cansee that the curve fits the data nicely. The coefficient of determination is r 2 � 0.99770, indicating a close fit and supporting the visual evidence.

Solve NumericallyTo predict the speed at impact, we substitute d � 1.80 into the obtainedpower regression model:

p�1.80� � 5.4.

See Figure 2.19c.

InterpretThe speed at impact is about 5.4 m�sec. This is slightly less than the valueobtained in Example 9 of Section 2.1, using a different modeling process forthe same experiment. Now try Exercise 57.


A Word of Warning

The regression routine traditionally used tocompute power function models involvestaking logarithms of the data, and therefore,all of the data must be strictly positive num-bers. So we must leave out (0, 0) to computethe power regression equation.

Why p?

We use p for speed to distinguish it fromvelocity v. Recall that speed is the absolutevalue of velocity.

Figure 2.19 Scatter plot and graphs for Example 6.

[–0.2, 2] by [–1, 6]

Y1=4.03X^(1/2)

X=1.8 Y=5.4068124

(c)[–0.2, 2] by [–1, 6]

(b)

[–0.2, 2] by [–1, 6]

(a)

In Exercises 1–6, write the following expressions using onlypositive integer powers.

1. x2�3 �3

x 2� 2. p5�2 �p 5�3. d�2 1�d 2

4. x�7 1/x 7

5. q�4�5 1��5

q 4� 6. m�1.5 1/�m 3�

In Exercises 7–10, write the following expressions in the formk • xa using a single rational number for the power a.

7. �9�x�3� 3x 3/28. �3 8�x�5� 2x 5/3

9. �3 � 1.71x –4/310. � 0.71x –1/2

4x��3�2�x�3�

5�x4

QUICK REVIEW 2.2 (For help, go to Section A.1.)

In Exercises 1–10, determine if the function is a power function,given that c, g, k, and � represent constants. For those that are,state the power and constant of variation. For those that are not,explain why not. If function notation is not used, name theindependent variable.

1. f �x� � ��12

� x52. f �x� � 9x5�3

3. f �x� � 3 • 2x4. f �x� �13

5. E�m� � mc26. KE�v� � �

12

� kv5

7. d � �12

� gt2 8. V � �43

� �r3

9. I � �dk2� 10. F(a) � m • a


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 29


In Exercises 11–16, determine if the function is a monomialfunction, given that l and � represent constants. For those thatare, state the degree and leading coefficient. For those that arenot, explain why not. If function notation is not used, name theindependent variable.

11. f �x� � �4 12. f �x� � 3x�5

13. y � �6x714. y � �2 � 5x

15. S� 4�r216. A � lw

In Exercises 17–22, write the statement as a power functionequation. Use k for the constant of variation if one is not given.

17. The area A of an equilateral triangle varies directly as thesquare of the length s of its sides.A � ks 2

18. The volume V of a circular cylinder with fixed height isproportional to the square of its radius r. V � kr2

19. The current I in an electrical circuit is inversely proportionalto the resistance R, with constant of variation V. I � V/R

20. Charles’s Law states the volume V of an enclosed ideal gas at aconstant pressure varies directly as the absolute temperature T.V � kT

21. The energy E produced in a nuclear reaction is proportionalto the mass m, with the constant of variation being c2, thesquare of the speed of light. E � mc2

22. The speed p of a free-falling object that has been droppedfrom rest varies as the square root of the distance traveled d,with a constant of variation k � �2�g�. p � �2gd�

In Exercises 23–26, write a sentence that expresses therelationship in the formula, using the language of variationor proportion.

23. w � mg, where w and m are the weight and mass of anobject and g is the constant acceleration due to gravity.

24. C � �D, where C and D are the circumference and diameterof a circle and � is the usual mathematical constant.

25. n � c�v, where n is the refractive index of a medium,v is the velocity of light in the medium, and c is the constantvelocity of light in free space.

26. d � p2��2g�, where d is the distance traveled by a free-fallingobject dropped from rest,p is the speed of the object, andg is the constant acceleration due to gravity.

In Exercises 27–28, data are given for y as a power function ofx.Write an equation for the power function, and state its powerand constant of variation.

27.

28.

In Exercises 29–34, match the equation to one of the curveslabeled in the figure.

29. f �x� � ��23

� x4 (g) 30. f �x� � �12

� x�5 (a)

31. f �x� � 2x1�4 (d) 32. f �x� � �x5�3 (g)33. f �x� � �2x�2 (h) 34. f �x� � 1.7x2�3 (d)

In Exercises 35–40, describe how to obtain the graph of thegiven monomial function from the graph of g �x� � xn with thesame power n. State whether f is even or odd. Sketch the graphby hand and support your answer with a grapher.

35. f �x� � �23

� x436. f �x� � 5x3

37. f �x� � �1.5x538. f �x� � �2x6

39. f �x� � �14

� x840. f �x� � �

18

� x7

In Exercises 41–44, state the power and constant of variation forthe function, graph it, and analyze it in the manner of Example 2of this section.

41. f �x� � 2x442. f �x� � �3x3

43. f �x� � �12

� �4 x� 44. f �x� � �2x�3

In Exercises 45–50, state the values of the constants k and afor the function f �x� � k • xa. Describe the portion of thecurve that lies in Quadrant I or IV. Determine whether f iseven, odd, or undefined for x 0. Describe the rest of thecurve if any. Graph the function to see whether it matches thedescription.

45. f �x� � 3x1�446. f �x� � �4x2�3

47. f �x� � �2x4�348. f �x� � �

25

� x5�2

49. f �x� � �12

� x�350. f �x� � �x�4

y

x

a

h

b

g

c

d

f

e

x 1 4 9 16 25y �2 �4 �6 �8 �10

x 2 4 6 8 10y 2 0.5 0.222. . . 0.125 0.08

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 30


51. Boyle’s Law The volume of an enclosed gas (at a constanttemperature) varies inversely as the pressure. If the pressureof a 3.46-L sample of neon gas at 302°K is 0.926 atm, whatwould the volume be at a pressure of 1.452 atm if thetemperature does not change? 2.21 L

52. Charles’s Law The volume of an enclosed gas (at a constantpressure) varies directly as the absolute temperature. If thepressure of a 3.46-L sample of neon gas at 302°K is0.926 atm, what would the volume be at a temperature of338°K if the pressure does not change?3.87L

53. Diamond Refraction Diamonds have the extremely highrefraction index of n � 2.42 on average over the range ofvisible light. Use the formula from Exercise 25 and the factthat c � 3.00� 108 m/sec to determine the speed of lightthrough a diamond. 1.24 � 108 m/sec

54. Windmill Power The power P (in watts) produced by awindmill is proportional to the cube of the wind speed v(in mph). If a wind of 10 mph generates 15 watts of power,how much power is generated by winds of 20, 40, and80 mph? Make a table and explain the pattern.

55. Keeping Warm For mammals and other warm-blooded animals to stay warm requires quite a bit ofenergy. Temperature loss is related to surface area, whichis related to body weight, and temperature gain is relatedto circulation, which is related to pulse rate. In thefinal analysis, scientists have concluded that the pulse rater of mammals is a power function of their body weight w.(a) Draw a scatter plot of the data in Table 2.12.

(b) Find the power regression model.

(c) Superimpose the regression curve on the scatter plot.

(d) Use the regression model to predict the pulse rate for a450-kg horse. Is the result close to the 38 beats/min reportedby A. J. Clark in 1927?

56. Even and Odd Functions If n is an integer,n 1, provethat f �x� � xn is an odd function if n is odd and is an evenfunction if n is even.

57. Light Intensity Velma and Reggie gathered the datain Table 2.13 using a 100-watt light bulb and a Calculator-Based LaboratoryTM (CBLTM) with a light-intensity probe.(a) Draw a scatter plot of the data in Table 2.13

(b) Find the power regression model. Is the power closeto the theoretical value of a � �2?


(d) Use the regression model to predict the light intensityat distances of 1.7m and 3.4 m.

Standardized Test Questions58. True or False The function f �x� � x�2�3 is even. Justify your

answer.

59. True or False The graph f �x� � x1�3 is symmetric about they-axis. Justify your answer.

In Exercises 60–63, solve the problem without using a calculator.

60. Let f �x� � 2x�1�2. What is the value of f �4�? (a)

(a) 1 (b) �1 (c) 2�2� (d) �2�

1

2�� (e) 4

61. Let f �x� � �3x�1�3. Which of the following statements istrue?

(a) f �0� � 0 (b) f ��1� � �3 (c) f �1� � 1

(d) f �3� � 3 (e) f �0� is undefined (e)

62. Let f �x� � x2�3. Which of the following statements is true?

(a) f is an odd function.

(b) f is an even function.

(c) f is neither an even nor an odd function.

(d) The graph f is symmetric with respect to the x-axis.

(e) The graph f is symmetric with respect to the origin.(b)

63. Which of the following is the domain of the functionf �x� � x3�2?

(a) All reals (b) 0,∞� (c) �0,∞�(d) ��∞,0� (e) ��∞,0� � �0,∞� (b)

Table 2.13 Light Intensity Data for

a 100-W Light Bulb

Distance Intensity(m) (W/m2)

1.0 7.951.5 3.532.0 2.012.5 1.273.0 0.90

Table 2.12 Weight and Pulse Rate of

Selected Mammals

Mammal Body weight (kg) Pulse rate(beats/min)

Rat 0.2 420Guinea pig 0.3 300Rabbit 2 205Small dog 5 120Large dog 30 85Sheep 50 70Human 70 72

Source: A. J. Clark, Comparative Physiology of the Heart.New York: Macmillan, 1927.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 31

Explorations64. Group Activity Rational Powers Working in a group of

three students, investigate the behavior of power functionsof the form f �x� � k • xm�n, where m and n are positive withno factors in common. Have one group member investigateeach of the following cases:

• n is even

• n is odd and m is even

• n is odd and m is odd

For each case, decide whether f is even,f is odd, or f isundefined for x 0. Solve graphically and confirmalgebraically in a way to convince the rest of your groupand your entire class.

65. Comparing the Graphs of Power Functions Graph thefunctions in the stated windows and explain how the graphsare alike and how they are different. Consider the relevantaspects of analysis from Example 2. Which ordered pairs doall four graphs have in common?

(a) f �x� � x�1, g�x� � x�2, h�x� � x�3, and k�x� � x�4 inthe windows [0, 1] by [0, 5], [0, 3] by [0, 3], and [�2, 2] by[�2, 2].

(b) f �x� � x1�2, g�x� � x1�3, h�x� � x1�4, and k�x� � x1�5 in thewindows [0, 1] by [0, 1], [0, 3] by [0, 2], and [�3, 3] by[�2, 2].

Extending the Ideas66. Writing to Learn Irrational Powers A negative number to

an irrational power is undefined. Analyze the graphs of f �x� � x�, x1��, x��, �x�, �x1��, and�x��. Prepare asketch of all six graphs on one set of axes, labeling each ofthe curves. Write an explanation for why each graph is posi-tioned and shaped as it is.

67. Planetary Motion Revisited Convert the time and distanceunits in Table 2.10 to the Earth-based units of years andastronomical units using

1 yr � 365.2 days and 1 AU� 149.6 Gm.

Use this “re-expressed” data to obtain a power functionmodel. Show algebraically that this model closely approxi-mates Kepler’s equation T2 � a3.

68. Free Fall Revisited The p of an object is theabsolute value of its velocity v. The distance traveled d byan object dropped from an initial height s0 with a currentheight s is given by

d � s0 � s

until it hits the ground. Use this information and the free-fall motion formulas from Section 2.1 to prove that

d � �12

� gt2, p � gt, and therefore p � �2�g�d�.

Do the results of Example 6 approximate this last formula?

69. Prove that g�x� � 1�f �x� is even if and only if f �x� is evenand that g(x) � 1�f �x� is odd if and only if f �x� is odd.

70. Use the results in Exercise 69 to prove that g(x) � k • x�a

is even if and only if f �x� � k • xa is even and thatg(x) � k • x�a is odd if and only if f �x� � k • xa is odd.

71. Joint Variation If a variable z varies as the product of thevariables x and y, we say z as x and y, andwe write z � k • x • y, where k is the constant of variation.Write a sentence that expresses the relationship in each ofthe following formulas, using the language of joint variation.

(a) F � m • a, where F and a are the force and accelerationacting on an object of mass m.

(b) KE � �1�2�m • v2, where KE and v are the kinetic energyand velocity of an object of mass m.

(c) F � G • m1 • m2�r 2, where F is the force of gravity actingon objects of masses m1 and m2 with a distance r betweentheir centers and G is the universal gravitational constant.

varies jointly

speed


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 32

Graphs of Polynomial FunctionsAs we saw in Section 2.1, a polynomial function of degree 0 is a constantfunction and graphs as a horizontal line. A polynomial function of degree 1 isa linear function; its graph is a slant line. A polynomial function of degree 2is a quadratic function; its graph is a parabola.

We now consider polynomial functions of higher degree. These include(polynomials of degree 3) and (poly-

nomials of degree 4). Recall that a polynomial function of degree n can bewritten in the form

f �x� � anxn � an�1xn�1 � . . . � a2x2 � a1x � a0, an � 0.

Here are some important definitions associated with polynomial functionsand this equation.

quartic functionscubic functions

In Example 1 we use both the fact that the constant term a0 of a polynomialfunction p is the initial value of the function p�0� and the y-intercept of thegraph to provide a quick and easy check of the transformed graphs.

EXAMPLE 1 Graphing transformations of monomialfunctions

Describe how to transform the graph of an appropriate monomial functionf �x� � anxn into the graph of the given function. Sketch the transformedgraph by hand and support your answer with a grapher. Compute thelocation of the y-intercept as a check on the transformed graph.

(a) g�x� � 4�x � 1�3 (b) h�x� � ��x � 2�4 � 5

SOLUTION(a) You can obtain the graph of g�x� � 4�x � 1�3 by shifting the graph off �x� � 4x3 one unit to the left, as shown in Figure 2.20a. The y-intercept ofthe graph of g is g�0� � 4�0 � 1�3 � 4, which appears to agree with thetransformed graph.

SECTION 2.3 Polynomial Functions of Higher Degree with Modeling 33

What you’ll learn about■ Graphs of Polynomial Functions■ End Behavior of Polynomial

Functions■ Zeros of Polynomial Functions■ Intermediate Value Theorem■ Modeling

. . . and whyThese topics are important inmodeling and can be used toprovide approximations to morecomplicated functions, as you willsee if you study calculus.

2.3 POLYNOMIAL FUNCTIONS OF HIGHER DEGREE

WITH MODELING

OBJECTIVEStudents will be able to graph polyno-mial functions, predict their end behav-ior, and find their real zeros using agrapher or an algebraic method.

MOTIVATEAsk students to describe the graphs ofpolynomial functions of degree 4.

LESSON GUIDEDay 1: Graphing; End BehaviorDay 2: Zeros; Intermediate ValueTheorem; Modeling

Definitions The Vocabulary of Polynomials• Each monomial in this sum—anxn, an�1xn�1, . . . ,a0—is a of

the polynomial.

• A polynomial function written in this way, with terms in descendingdegree, is written in .

• The constants an, an�1, . . . ,a0 are the of the polynomial.

• The term anxn is the , and a0 is the constant term.leading term

coefficients

standard form

term

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 33

(b) You can obtain the graph of h �x� � ��x � 2�4 � 5 by shifting the graphof f �x� � �x4 two units to the right and five units up, as shown inFigure 2.20b. The y-intercept of the graph of h is h�0� � ��0 � 2�4 � 5 ��16 � 5 � �11, which appears to agree with the transformed graph.

Example 2 shows what can happen when simple monomial functions arecombined to obtain polynomial functions. The resulting polynomials are notmere translations of monomials.

EXAMPLE 2 Graphing combinations of monomialfunctions

Graph the polynomial function, locate its extrema and zeros, and explainhow it is related to the monomials from which it is built.

(a) f �x� � x3 � x (b) g�x� � x3 � x

SOLUTION(a) The graph of f �x� � x3 � x is shown in Figure 2.21a. The function f isincreasing on (��, �) no extrema and one zero located at x � 0. The func-tion factors as f �x� � x�x2 � 1� and has one zero at x � 0.

The general shape of the graph is much like the graph of its leading term x3,but near the originf behaves much like its other term x, as seen in Figure 2.21b.The function f is odd, just like its two building block monomials.

(b) The graph of g�x� � x3 � x is shown in Figure 2.22a. The function g hasa local maximum of about 0.38 at x � �0.58 and a local minimum of about�0.38 at x � 0.58. The function factors as g�x� � x�x � 1��x � 1� and haszeros located at x � �1, x � 0, and x � 1.

The general shape of the graph is much like the graph of its leading termx3, but near the origin g behaves much like its other term �x, as seen inFigure 2.22b. The function g is odd, just like its two building blockmonomials.

Figure 2.21 The graph of f (x) � x3 � x (a) by itself and (b) with y � x. (Example 2a)

We have now seen a few examples of graphs of polynomial functions, but arethese typical? What do graphs of polynomials look like in general?

[–4.7, 4.7] by [–3.1, 3.1]

(b)

[–4.7, 4.7] by [–3.1, 3.1]

(a)

Now try Exercise 7.

Now try Exercise 3.


Figure 2.20 (a) The graphs ofg(x) � 4(x � 1)3 and f (x) � 4x3.(b) The graphs of h (x) � �(x � 2)4 � 5 andf (x) � �x 4. (Example 1)

y

(b)

108642

–4–2

–6–8

–10

–5 –4 –3 –2

–12–14

x5432

y

(a)

10864

–4–6–8

–10

–5 –4 –3 –2x

54321

TEACHING NOTENote for Example 2: You may wish tohave students graph y � x 3 and y � x 3 � x on the same axes. Similarly,for y � x 3 and y � x 3 � x.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 34

Figure 2.22 The graph of g(x) � x3 � x (a) by itself and (b) with y � �x.(Example 2b)

To begin our answer, let’s first recall that every polynomial function is definedand continuous for all real numbers. Not only are graphs of polynomialsunbroken without jumps or holes, but they are smooth, unbroken lines orcurves, with no sharp corners or cusps. Typical graphs of cubic and quarticfunctions are shown in Figures 2.23 and 2.24.

Figure 2.23 Graphs of four typical cubic functions: (a) two with positive and(b) two with negative leading coefficients.

Imagine horizontal lines passing through the graphs in Figures 2.23 and 2.24,acting as x-axes. Each intersection would be an x-intercept that would corre-spond to a zero of the function. From this mental experiment, we see that cubicfunctions have at most three zeros and quartic functions have at most four zeros.

Focusing on the high and low points in Figures 2.23 and 2.24, we see thatcubic functions have at most two local extrema and quartic functions have atmost three local extrema. The following can be proved in calculus:

End Behavior of Polynomial FunctionsAn important characteristic of polynomial functions is their end behavior. As weshall see, the end behavior of a polynomial is closely related to the end behavior

Theorem Local Extrema and Zeros of Polynomial FunctionsA polynomial function of degree n has at most n � 1 local extrema andat most n zeros.

(b)

a3 < 0

(a)

a3 > 0

[–4.7, 4.7] by [–3.1, 3.1]

(b)

[–4.7, 4.7] by [–3.1, 3.1]

(a)


TEACHING NOTEYou may wish to tell students that weuse the informal word smooth todescribe functions that will be calleddifferentiable in calculus.

Technology Note

For a cubic, when you change the horizontalwindow by a factor of k, it usually is a goodidea to change the vertical window by afactor of k3. Similar statements can be madeabout polynomials of other degrees.

Figure 2.24 Graphs of four typicalquartic functions: (a) two with positive and(b) two with negative leading coefficients.

(b)

a4 < 0

(a)

a4 > 0

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 35

of its leading term. The leading term of a polynomial of degree n is a monomialof degree n. Exploration 1 examines the end behavior of monomial functions.

Example 3 illustrates the link between the end behavior of a polynomialf �x� � anxn � . . . � a1x � a0 and its leading term anxn.

EXAMPLE 3 Comparing the graphs of a polynomialand its leading term

Superimpose the graphs of f �x� � x3 � 4x2 � 5x � 3 and g�x� � x3 in suc-cessively larger viewing windows, a process called . Continuezooming out until the graphs look nearly identical.

SOLUTION Figure 2.25 shows three views of the graphs of f �x� �x3 � 4x2 � 5x � 3 and g�x� � x3 in progressively larger viewing windows.As the dimensions of the window increase it gets harder to tell them apart.Moreover,

limx→∞

f �x� � limx→∞

g�x� � ∞ and limx→�∞

f �x� � limx→�∞

g�x� � �∞.

Example 3 illustrates something that is true for all polynomials:In sufficientlylarge viewing windows, the graph of a polynomial and the graph of its leadingterm appear to be identical.Said another way, the leading term dominatesthebehavior of the polynomial as �x� → ∞. Based on this fact and what we haveseen in Exploration 1, there are four possible end behavior patterns for a poly-nomial function. The power and coefficient of the leading term tell us whichone of the four patterns occurs.

EXAMPLE 4 Applying polynomial theoryGraph the polynomial in a window showing its extrema and zeros and itsend behavior. Describe the end behavior using limits.


zoom out


Investigating the End Behavior of f (x) � anxn

Graph each function in the window �5, 5� by �15, 15�. Describethe end behavior using lim

x→∞f �x� and lim

x→�∞f �x�.

1. (a) f �x� � 2x3 (b) f �x� � �x3

(c) f �x� � x5 (d) f �x� � �0.5x7

2. (a) f �x� � �3x4 (b) f �x� � 0.6x4

(c) f �x� � 2x6 (d) f �x� � �0.5x2

3. (a) f �x� � �0.3x5 (b) f �x� � �2x2

(c) f �x� � 3x4 (d) f �x� � 2.5x3

Describe the patterns you observe. In particular, how do the valuesof the coefficient an and the degree n affect the end behavior off �x� � anxn?

EXPLORATION 1

EXPLORATION EXTENSIONSGraph the functions f (x) � 2x3 � x2,f (x) � �x3 � 2, f (x) � �3x4 � 2x3, andf (x) � 0.6x4 � 5x and compare the endbehavior with the functions in question 1.Adjust the viewing window if necessary.

Figure 2.25 As the viewing window getslarger, the graphs of f (x) � x3 � 4x2 � 5x � 3and g(x) � x3 look more and more alike.(Example 3)

[–56, 56] by [–12800, 12800]

(c)

[–14, 14] by [–200, 200]

(b)

[–7, 7] by [–25, 25]

(a)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 36

(a) f �x� � x3 � 2x2 � 11x � 12

(b) g�x� � 2x4 � 2x3 � 22x2 � 18x � 35

SOLUTION

(a) The graph of f �x� � x3 � 2x2 � 11x � 12 is shown in Figure 2.26a. Thefunction f has 2 extrema and 3 zeros, the maximum number possible for acubic. lim

x→∞f �x� � ∞ and lim

x→�∞f �x� � �∞.

(b) The graph of g�x� � 2x4 � 2x3 � 22x2 � 18x � 35 is shown in Figure2.26b. The function g has 3 extrema and 4 zeros, the maximum number pos-sible for a quartic. lim

x→∞g�x� � ∞ and lim

x→�∞g�x� � ∞.

Zeros of Polynomial FunctionsRecall that finding the real-number zeros of a function f is equivalent to find-ing the x-intercepts of the graph of y � f �x� or the solutions to the equationf �x� � 0. Example 5 illustrates that factoring a polynomial function makessolving these three related problems an easy matter.



Leading Term Test for Polynomial End BehaviorFor any polynomial function f �x� � anxn � � � � � a1x � a0, the limitslimx→∞

f �x� and limx→�∞

f �x� are determined by the degree n of the

polynomial and its leading coefficient an:

y

xan > 0n odd

an < 0n odd

an > 0n even

an < 0n even

lim f(x) = �x→�

lim f(x) = –�x→–�

y

x

lim f(x) = –�x→�

lim f(x) = �x→–�

y

x

lim f(x) = �x→�

lim f(x) = �x→–�

y

x

lim f(x) = –�x→–�

lim f(x) = –�x→�

Figure 2.26 (a) f (x) � x3 � 2x2 � 11x � 12,(b) g(x) � 2x4 � 2x3 � 22x2 � 18x � 35.(Example 4)

[–5, 5] by [–50, 50]

(b)

[–5, 5] by [–25, 25]

(a)

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 37

EXAMPLE 5 Finding the zeros of a polynomial functionFind the zeros of f �x� � x3 � x2 � 6x.

SOLUTIONSolve AlgebraicallyWe solve the related equation f �x� � 0 by factoring:

x3 � x2 � 6x � 0

x�x2 � x � 6� � 0 Remove common factor x.

x�x � 3��x � 2� � 0 Factor quadratic.

x � 0, x � 3 � 0, or x � 2 � 0 Zero factor property

x � 0, x � 3, or x � �2

So the zeros of f are 0, 3, and �2.

Solve GraphicallyUse the features of your calculator to approximate the zeros of f. Figure 2.27shows that there are three values. Based on our algebraic solution we can besure that these values are exact.

From Example 5, we see that if a polynomial function f is presented in factoredform, each factor �x � k� corresponds to a zero x � k, and if k is a real number,�k, 0� is an x-intercept of the graph of y � f �x�. We apply this principle inExample 6.

When a factor is repeated, as in f �x� � �x � 2�3�x � 1�2, we say the polynomialfunction has a repeated zero. The function f has two repeated zeros. Becausethe factor x � 2 occurs three times, 2 is a zero of multiplicity 3. Similarly,�1is a zero of multiplicity 2. The following definition generalizes this concept.

A zero of multiplicity m 2 is a . Notice in Figure 2.28 thatthe graph of f just kissesthe x-axis without crossing it at ��1, 0�, but that thegraph of f crosses the x-axis at �2, 0�. This too can be generalized.

Zeros of Odd and Even MultiplicityIf a polynomial functionf has a real zero c of odd multiplicity, then thegraph off crosses the x-axis at �c, 0� and the value off changes sign atx � c.

If a polynomial functionf has a real zero c of even multiplicity, then thegraph off does not cross the x-axis at �c, 0� and the value off does notchange sign at x � c.

repeated zero



Figure 2.27 The graph of y � x3 � x2 �

6x showing the x-intercepts. (Example 5)

[–5, 5] by [–15, 15]

(–2, 0) (0, 0) (3, 0)

Figure 2.28 The graph of f (x) �

(x � 2)3(x � 1)2 showing the x-intercepts.

[–4, 4] by [–10, 10]

TEACHING NOTEDiscuss the terminology and notationassociated with zeros of a function:x-intercept, root, and solution.

Definition Multiplicity of a Zero of a Polynomial FunctionIf f is a polynomial function and �x � c�m is a factor off but �x � c�m�1

is not, then c is a zero of off.multiplicity m

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 38

In Example 5 none of the zeros were repeated. Because a nonrepeated zerohas multiplicity 1, and 1 is odd, the graph of a polynomial function crossesthe x-axis and has a sign change at every nonrepeated zero (Figure 2.27).Knowing when a graph crosses the x-axis and when it doesn’t is important incurve-sketching and in solving inequalities.

EXAMPLE 6 Sketching the graph of a factoredpolynomial

State the degree and list the zeros of the function f �x� � �x � 2�3�x � 1�2.State the multiplicity of each zero and whether the graph crosses the x-axisat the corresponding x-intercept. Then sketch the graph of f by hand.

SOLUTIONThe degree of f is 5 and the zeros are x � �2 and x � 1. The multiplicity ofthe zero x � �2 is 3 and the graph crosses the x-axis at x � �2 because themultiplicity 3 is odd. The multiplicity of the zero x � 1 is 2. The graph istangent to the x-axis at x � 1 because the multiplicity 2 is even. Notice thatvalues of f are positive for x 1, positive for �2 x 1 , and negative forx �2. Figure 2.29 shows a sketch of the graph of f.

Intermediate Value TheoremThe Intermediate Value Theoremtells us that a sign change implies a real zero.

EXAMPLE 7 Using the intermediate value theoremProve that every polynomial function of odd degree has at least one real zero.

SOLUTION Let f be a polynomial function of odd degree. Because f is odd,the leading term test tells us that lim

x→∞ f �x� � �lim

x→�∞ f �x�. So there exist real

numbers a and b with a b and such that f �a� and f �b� have opposite signs.Because every polynomial function is defined and continuous for all realnumbers, f is continuous on the interval [a, b]. Therefore, by theIntermediate Value Theorem,f � c� � 0 for some number c in [a, b], and thusc is a real zero of f. Now try Exercise 61.

Theorem Intermediate Value TheoremIf a and b are real numbers with a b and if f is continuous on the inter-val a, b�, then f takes on every value betweenf �a� and f �b�. In otherwords, if y0 is betweenf �a� and f �b�, then y0 � f �c� for some number cin a, b�.

In particular, if f �a� and f �b� have opposite signs (i.e., one is negativeand the other is positive), thenf �c� � 0 for some number c in a, b�(Figure 2.30).



Figure 2.29 A sketch of the graph off (x) � (x � 2)3(x � 1)2 showing the x-intercepts.

y

10

642

–4–2

–6–8

–10

–5 –4 –3 –2 –1x

54321

ALERTSome students fail to make the distinc-tion between exact and approximateanswers. They may think that �3�(exact) and 1.732 (approximate) areequivalent.

Figure 2.30 If f (a) 0 f (b), thenthere is a zero x � c between a and b.

y

f (a)

f (b)

y0 � 0

c

a

bx

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 39

In practice, the Intermediate Value Theorem is used in combination with ourother mathematical knowledge and technological know-how.

EXAMPLE 8 Zooming to uncover hidden behaviorFind all of the real zeros of f �x� � x4 � 0.1x3 � 6.5x2 � 7.9x � 2.4.

SOLUTIONSolve GraphicallyBecause f is of degree 4, there are at most four zeros. The graph inFigure 2.31a suggests a single zero (multiplicity 1� around x � �3 and atriple zero (multiplicity 3� around x � 1. Closer inspection around x � 1 inFigure 2.31b reveals three separate zeros. Using the grapher, we find thefour zeros to be x � 1.37,x � 1.13,x � 0.50, and x � �3.10.

ModelingIn the problem-solving process presented in Section 1.1, Step 2 is to developa mathematical model of the problem. When the model being developed is apolynomial function of higher degree, the algebraic and geometric thinkingrequired can be rather involved. In solving Example 9 you may find it helpfulto make a physical model out of paper or cardboard.

EXAMPLE 9 Designing a boxDixie Packaging Company has contracted to make boxes with a volume ofapproximately 484 in.3. Squares are to be cut from the corners of a 20-in. by 25-in. piece of cardboard, and the flaps folded up to make an openbox. (See Figure 2.32.� What size squares should be cut from the cardboard?

SOLUTIONModelWe know that the volume V � height � length � width. So let

x � edge of cut-out square (height of box)

25 � 2x � length of the box

20 � 2x � width of the box

V � x�25 � 2x��20 � 2x�

Solve Numerically and GraphicallyFor a volume of 484, we solve the equation x�25 � 2x��20 � 2x� � 484.Because the width of the cardboard is 20 in., 0� x � 10. We use the tablein Figure 2.33 to get a sense of the volume values to set the window for thegraphs in Figure 2.34. The cubic volume function intersects the constantvolume of 484 at x � 1.22 and x � 6.87.



Figure 2.31 (Example 8)

(b)

[0, 2] by [–0.5, 0.5]

[–5, 5] by [–50, 50]

(a)

Figure 2.32 Cut square corners from apiece of cardboard, and fold the flaps tomake a box. (Example 9)

x

x

25

20

Figure 2.33 A table to get a feel for thevolume values in Example 9.

X

Y1 = X(20–2X)(25–...

1234567

414672798816750624462

Y1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 40

InterpretSquares with lengths of approximately 1.22 in. or 6.87 in. should be cutfrom the cardboard to produce a box with a volume of 484 in.3.

Just as any two points in the Cartesian plane with different x values anddifferent y values determine a unique slant line and its related linear function,any three noncollinear points with different x values determine a quadraticfunction. In general,�n � 1� points positioned with sufficient generalitydetermine a polynomial function of degree n. The process of fitting apolynomial of degree n to �n � 1� points is .Exploration 2 involves two polynomial interpolation problems.

polynomial interpolation



Figure 2.34 y1 � x(25 � 2x)(20 � 2x)and y2 � 484. (Example 9)

[0, 10] by [0, 1000]

EXPLORATION EXTENSIONSNow use a quadratic regression to fitthe four points in Step 1 and a cubicregression to fit the five points in Step 2. How does this affect the fit ineach case? Why?

FOLLOW-UPAsk students to discuss the possiblenumber of real zeros for a degree 5polynomial. (1, 2, 3, 4, or 5)

ASSIGNMENT GUIDEDay 1: Ex. 3, 6, 15–36, multiples of 3Day 2: Ex. 9, 12, 39–54, multiples of 3, 58,59, 63, 65, 66, 75, 83, 85

COOPERATIVE LEARNINGGroup Activity: Ex. 86NOTES ON EXERCISESEx. 17–28, 43–48, and 75–80 are designedto emphasize the importance of usingan appropriate viewing window on thegrapher.Ex. 63–68 offer a variety of applications.Remind students to use the language ofmodels appropriately.Ex. 69–74 provide practice withstandardized tests.Ex. 83–84 are related to the calculustopic of taking derivatives.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 7, 15, 19, 33, 41, 61,63, 67, 75Embedded Assessment: Ex. 36, 59, 75

Generally we want a reason beyond “it fits good” to choose a model forgenuine data. However, when no theoretical basis exists for picking a model,a balance between goodness of fit and simplicity of model is sought. Forpolynomials, we try to pick a model with the lowest possible degree that hasa reasonably good fit.

Table 2.14 U.S. Farm Exports

Year Amount (billions)

1980 41.21985 29.01990 39.51992 43.21993 42.91994 46.31995 56.31996 60.41997 57.21998 51.81999 48.52000 51.6

Source: U.S. Department of Agriculture, Statistical Abstractof the United States, 2001 (Washington, D. C., 2001)

Interpolating Points with a Polynomial1. Use cubic regression to fit a curve through the four points given in

the table.

x �2 1 3 8

y 2 0.5 �0.2 1.25

2. Use quartic regression to fit a curve through the five points givenin the table.

x 3 4 5 6 8

y �2 �4 �1 8 3

How good is the fit in each case? Why?

EXPLORATION 2

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 41

In Exercises 1–6, describe how to transform the graph of anappropriate monomial function f �x� � xn into the graph of thegiven polynomial function. Sketch the transformed graph byhand and support your answer with a grapher. Compute thelocation of the y-intercept as a check on the transformed graph.

1. g�x� � 2�x � 3�32. g�x� � ��x � 5�3

3. g�x� � ��12

� �x � 1�3 � 2 4. g�x� � �23

� �x � 3�3 � 1

5. g�x� � �2�x � 2�4 � 3 6. g�x� � 3�x � 1�4 � 2

In Exercises 7 and 8, graph the polynomial function, locate itsextrema and zeros, and explain how it is related to the monomi-als from which it is built.

7. f �x� � �x4 � 2x 8. g�x� � 2x4 � 5x2

EXAMPLE 10 Modeling data curve fittingTable 2.14 shows the total U.S. Farm Exports in billions for several years.Try various polynomial regression models (degrees n � 1, 2, 3, 4) anddecide which is the best model.

Figure 2.35 Scatter plot and cubic regression graph for Example 10.

SOLUTIONLet x � 0 represent the year 1980,x � 1 the year 1981, and so on. Makinga scatter plot of the data and superimposing the polynomial regression func-tions of degrees n � 1, 2, 3, 4 leads us to the conclusion that the cubicmodel

y � �0.0276x3 � 0.9036x2 � 6.6274x � 41.6526

does the best job of balancing goodness of fit with lowest possible degree.See Figure 2.35. Now try Exercise 63.

[–5, 25] by [0, 70]


In Exercises 1–6, factor the polynomial into linear factors.

1. x2 � x � 12 �x � 4��x � 3� 2. x2 � 11x � 28

3. 3x2 � 11x � 6 4. 6x2 � 5x � 1

5. 3x3 � 5x2 � 2x 6. 6x3 � 22x2 � 12x

In Exercises 7–10, solve the equation mentally.

7. x�x � 1� � 0 x � 0, x � 1 8. x�x � 2��x � 5� � 0

9. �x � 6�3�x � 3��x � 1.5� � 0 x � �6, x � �3, x � 1.5

10. �x � 6�2�x � 4�4�x � 5�3 � 0 x � �6, x � �4, x � 5

QUICK REVIEW 2.3 (For help, go to Sections A.2 and P.5.)


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 42

In Exercises 9–12, match the polynomial function with its graph.Explain your choice. Do not use a graphing calculator.

9. f �x� � 7x3 � 21x2 � 91x � 104 (c)

10. f �x� � �9x3 � 27x2 � 54x � 73 (b)

11. f �x� � x5 � 8x4 � 9x3 � 58x2 � 164x � 69 (a)

12. f �x� � �x5 � 3x4 � 16x3 � 2x2 � 95x � 44 (d)

In Exercises 13–16, graph the function pairs in the same seriesof viewing windows. Zoom out until the two graphs look nearlyidentical and state your final viewing window.

13. f �x� � x3 � 4x2 � 5x � 3 and g�x� � x3

14. f �x� � x3 � 2x2 � x � 5 and g�x� � x3

15. f �x� � 2x3 � 3x2 � 6x � 15 and g�x� � 2x3

16. f �x� � 3x3 � 12x � 17 and g�x� � 3x3

In Exercises 17–24, graph the function in a viewing window thatshows all of its extrema and x-intercepts. Describe the endbehavior using limits.

17. f �x� � �x � 1��x � 2��x � 3�18. f �x� � �2x � 3��4 � x��x � 1�19. f �x� � �x3 � 4x2 � 31x � 70

20. f �x� � x3 � 2x2 � 41x � 42

21. f �x� � �x � 2�2�x � 1��x � 3�22. f �x� � �2x � 1��x � 4�3

23. f �x� � 2x4 � 5x3 � 17x2 � 14x � 41

24. f �x� � �3x4 � 5x3 � 15x2 � 5x � 19

In Exercises 25–28, describe the end behavior of the polynomialfunction using lim

x→∞f �x� and lim

x→�∞f �x�.

25. f �x� � 3x4 � 5x2 � 3 ∞, ∞26. f �x� � �x3 � 7x2 � 4x � 3 �∞, ∞

27. f �x� � 7x2 � x3 � 3x � 4 �∞, ∞28. f �x� � x3 � x4 � 3x2 � 2x � 7 �∞, �∞In Exercises 29–32, match the polynomial function with itsgraph. Approximate all of the real zeros of the function.

29. f � x� � 20x3 � 8x2 � 83x � 55

30. f � x� � 35x3 � 134x2 � 93x � 18

31. f � x� � 44x4 � 65x3 � x2 � 17x � 3

32. f � x� � 4x4 � 8x3 � 19x2 � 23x � 6

In Exercises 33–38, find the zeros of the function algebraically.

33. f �x� � x2 � 2x � 8 34. f �x� � 3x2 � 4x � 4

35. f �x� � 9x2 � 3x � 2 36. f �x� � x3 � 25x

37. f �x� � 3x3 � x2 � 2x 38. f � x� � 5x3 � 5x2 � 10x

In Exercises 39–42, state the degree and list the zeros of thepolynomial function. State the multiplicity of each zero andwhether the graph crosses the x-axis at the correspondingx-intercept. Then sketch the graph of the polynomial functionby hand.

39. f � x� � x�x � 3�240. f �x� � �x3�x � 2�

41. f � x� � �x � 1�3�x � 2�242. f �x� � 7�x � 3�2�x � 5�4

In Exercises 43–48, graph the function in a viewing window thatshows all of its x-intercepts and approximate all of its zeros.

43. f �x� � 2x3 � 3x2 � 7x � 6

44. f �x� � �x3 � 3x2 � 7x � 2

45. f �x� � x3 � 2x2 � 4x � 7

46. f � x� � �x4 � 3x3 � 7x2 � 2x � 8

47. f �x� � x4 � 3x3 � 9x2 � 2x � 3

48. f �x� � 2x5 � 11x4 � 4x3 � 47x2 � 42x � 8

[–4, 4] by [–50, 50]

(d)

[–2, 2] by [–10, 50]

(c)

[–4, 4] by [–200, 200]

(b)

[–4, 4] by [–200, 200]

(a)

[–5, 6] by [–200, 400]

(d)

[–5, 6] by [–200, 400]

(c)

[–5, 6] by [–200, 400]

(b)

[–5, 6] by [–200, 400]

(a)


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 43

In Exercises 49–52, find the zeros of the function algebraicallyor graphically.

49. f �x� � x3 � 36x 0, �6, and 6

50. f �x� � x3 � 2x2 � 109x � 110 �11, �1, and 10

51. f �x� � x3 � 7x2 � 49x � 55 �5, 1, 11

52. f �x� � x3 � 4x2 � 44x � 96 �6, 2, and 8

In Exercises 53–56, using only algebra, find a cubic functionwith the given zeros. Support by graphing your answer.

53. 3, �4, 6 54. �2, 3,�5

55. �3�, ��3�, 4 56. 1, 1� �2�, 1 � �2�

57. Use cubic regression to fit a curve through the four pointsgiven in the table.

x �3 �1 1 3

y 22 25 12 �5

58. Use cubic regression to fit a curve through the four pointsgiven in the table.

x �2 1 4 7

y 2 5 9 26

59. Use quartic regression to fit a curve through the five pointsgiven in the table.

x 3 4 5 6 8

y �7 �4 �11 8 3

60. Use quartic regression to fit a curve through the five pointsgiven in the table.

x 0 4 5 7 13

y �21 �19 �12 8 3

In Exercises 61–62, explain why the function has at least onereal zero.

61. Writing to Learn f �x� � x7 � x � 100

62. Writing to Learn f �x� � x9 � x � 50

63. Stopping Distance A state highway patrol safety divisioncollected the data on stopping distances in Table 2.15.

(a) Draw a scatter plot of the data.

(b) Find the quadratic regression model.


(d) Use the regression model to predict the stopping distancefor a vehicle traveling at 25 mph.

(e) Use the regression model to predict the speed of a car ifthe stopping distance is 300 ft.

64. Analyzing Profit Economists for Smith Brothers, Inc., findthe company profit P by using the formula P � R � C,where R is the total revenue generated by the business andC is the total cost of operating the business.

(a) Using data from past years, the economists determinedthat R�x� � 0.0125x2 � 412x models total revenue, andC �x� � 12,225� 0.00135x3 models the total cost of doingbusiness, where x is the number of customers patronizingthe business. How many customers must Smith Bros. haveto be profitable each year?

(b) How many customers must there be for Smith Bros. torealize an annual profit of $60,000?

65. Circulation of Blood Researchconducted at a national healthresearch project shows that thespeed at which a blood cell travels in an artery depends on its distance from the center of the artery. The function v � 1.19� 1.87r 2 models thevelocity (in centimeters per second) of a cell that is rcentimeters from the center of an artery.

(a) Find a graph of v that reflects values of v appropriate forthis problem. Record the viewing-window dimensions.

(b) If a blood cell is traveling at 0.975 cm/sec, estimate thedistance the blood cell is from the center of the artery.

66. Volume of a Box Dixie Packaging Co. has contracted tomanufacture a box with no top that is to be made by remov-ing squares of width x from the corners of a 15-in. by 60-in.piece of cardboard.

(a) Show that the volume of the box is modeled by V � x� � x�60 � 2x� �15 � 2x�.

r

Table 2.15 Highway Safety Division

Speed (mph) Stopping Distance (ft)

10 15.120 39.930 75.240 120.550 175.9


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 44


(b) Determine x so that the volume of the box is at least450 in.3

67. Volume of a Box Squares of width x are removed from a 10-cm by 25-cm piece of cardboard, and the resulting edgesare folded up to form a box with no top. Determine all valuesof x so that the volume of the resulting box is at most 175 cm3.

68. Volume of a Box The function V � 2666x � 210x2 � 4x3

represents the volume of a box that has been made byremoving squares of width x from each corner of a rectangu-lar sheet of material and then folding up the sides. What val-ues are possible for x?

Standardized Test Questions69. True or False The graph of f �x� � x3 � x2 � 2 crosses the

x-axis between x � 1 and x � 2. Justify your answer.

70. True or False If the graph of g�x� � �x � a�2 is obtained bytranslating the graph of f �x� � x2 to the right, then a mustbe positive. Justify your answer.


71. What is the y-intercept of the graph of f �x� � 2(x � 1�3 � 5?

(a) 7 (b) 5 (c) 3 (d) 2 (e) 1 (c)

72. What is the multiplicity of the zero x � 2 in f �x� ��x � 2�2�x � 2�3�x � 3�7?

(a) 1 (b) 2 (c) 3 (d) 5 (e) 7 (b)

In Exercises 73–74, which of the specified functions might havethe given graph?

73. (b)

(a) f �x� � �x�x � 2��2 � x�(b) f �x� � �x�x � 2��x � 2�(c) f �x� � �x2�x � 2��x � 2�(d) f �x� � �x�x � 2�2�x � 2�(e) f � x� � �x�x � 2��x � 2�2

74. (a)

(a) f � x� � x�x � 2�2�x � 2�(b) f �x� � x�x � 2�2�2 � x�(c) f �x� � x2�x � 2��x � 2�(d) f �x� � x�x � 2��x � 2�2

(e) f �x� � x2�x � 2��x � 2�2

ExplorationsIn Exercises 75 and 76, two views of the function are given.

75. Writing to Learn Describe why each view of the function

f �x� � x5 � 10x4 � 2x3 � 64x2 � 3x � 55,

by itself, may be considered inadequate.

76. Writing to Learn Describe why each view of the function

f � x� � 10x4 � 19x3 � 121x2 � 143x � 51,

by itself, may be considered inadequate.

[0.5, 1.5] by [–1, 1]

(b)

[–6, 4] by [–2000, 2000]

(a)

[–3, 4] by [–250, 100]

(b)

[–5, 10] by [–7500, 7500]

(a)

y

–2x

2

y

–2x

2

60 in.

15 in.

xx

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 45

In Exercises 77–80, the function has hidden behavior whenviewed in the window �10, 10� by �10, 10�. Describe whatbehavior is hidden, and state the dimensions of a viewingwindow that reveals the hidden behavior.

77. f �x� � 10x3 � 40x2 � 50x � 20

78. f �x� � 0.5�x3 � 8x2 � 12.99x � 5.94�79. f �x� � 11x3 � 10x2 � 3x � 5

80. f �x� � 33x3 � 100x2 � 101x � 40

Extending the Ideas81. Graph the left side of the equation

3�x3 � x� � a�x � b�3 � c.

Then explain why there are no real numbers a, b, and cthat make the equation true. (Hint: Use your knowledge ofy � x3 and transformations.�

82. Graph the left side of the equation

x4 � 3x3 � 2x � 3 � a�x � b�4 � c.

Then explain why there are no real numbers a, b, and c thatmake the equation true.

83. Looking Ahead to Calculus The figure shows a graph ofboth f �x� � �x3 � 2x2 � 9x � 11 and the line L defined byy � 5�x � 2� � 7.

(a) Confirm that the point Q�2, 7� is a point of intersectionof the two graphs.

(b) Zoom in at point Q to develop a visual understanding thaty � 5�x � 2� � 7 is a linear approximationfor y � f �x� nearx � 2.

(c) Recall that a line is tangentto a circle at a point P ifit intersects the circle only at point P. View the two graphsin the window �5, 5� by �25, 25�, and explain why thatdefinition of tangent line is not valid for the graph of f.

84. Looking Ahead to Calculus Consider the function f �x� � xn

where n is an odd integer.

(a) Suppose that a is a positive number. Show that the slopeof the line through the points P�a, f �a�� and Q��a, f ��a��is an�1.

(b) Let x0 � a1��n�1�. Find an equation of the line throughpoint �x0, f �x0�� with the slope an�1.

(c) Consider the special case n � 3 and a � 3. Show boththe graph of f and the line from part b in the window�5, 5� by �30, 30�.

85. Derive an Algebraic Model of a Problem Show that thedistance x in the figure is a solution of the equation x4 � 16x3 � 500x2 � 8000x � 32,000� 0 and find thevalue of D by following these steps.

(a) Use the similar triangles in the diagram and the proper-ties of proportions learned in geometry to show that

�8x

� � �y �

y8

�.

(b) Show that y � �x

8�

x8

�.

(c) Show that y2 � x2 � 500. Then substitute for y, andsimplify to obtain the desired degree 4 equation in x.

(d) Find the distance D.

86. Group Learning Activity Work in groups of threeConsider functions of the form f �x� � x3 � bx2 � x � 1where b is a nonzero real number.

(a) Discuss as a group how the value of b affects the graphof the function.

(b) After completing (a), have each member of thegroup (individually) predict what the graphs of f �x� � x3 � 15x2 � x � 1 and g�x� � x3 � 15x2 � x � 1will look like.

(c) Compare your predictions with each other. Confirmwhether they are correct.

30

820

DD – u u

x

y

[0, 5] by [–10, 15]

(2, 7)


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 46

Long Division and the Division AlgorithmWe have seen that a polynomial in factored form reveals its zeros and muchabout its graph. Understanding the division of polynomials will give usnew and better ways to find factors. First we observe that the division of poly-nomials closely resembles the division of integers. Examine the followingside-by-side long divisions. How are they alike?

112 1x2 � 1x � 2 ← Quotient

32�3�5�8�7� 3x � 2�3�x�3�� 5�x�2�� 8�x�� 7� ← Dividend

32 3x3 � 2x2 ← Multiply: 1x2 • (3x � 2)

387 3x2 � 8x� 7 ← Subtract

32 3x2 � 2x ← Multiply: 1x • (3x � 2)

67 6x� 7 ← Subtract

64 6x� 4 ← Multiply: 2 • (3x � 2)

3 3 ← Remainder

Every division, whether integer or polynomial, involves a dividend divided bya divisor to obtain a quotientand a remainder. We can always check and sum-marize our result with an equation of the form

�Divisor��Quotient� � Remainder� Dividend.

For instance, in the example above, to check or summarize these long divi-sions we could write

32� 112� 3 � 3587 �3x � 2��x2 � x � 2� � 3 � 3x3 � 5x2 � 8x � 7.

The division algorithm contains such a summary polynomial equation, butwith the dividend written on the left side of the equation.

The function f �x� in the division algorithm is the , and d�x� is the. If r �x� � 0, we say d�x� into f �x�.

The summary statement (1) is sometimes written in fraction formas follows.

�df �

�xx��

� � q�x� � �rd��xx��

� (2)

divides evenlydivisordividend

SECTION 2.4 Real Zeros of Polynomial Functions 47

What you’ll learn about■ Long Division and the Division

Algorithm■ Remainder and Factor Theorems■ Synthetic Division■ Rational Zeros Theorem■ Upper and Lower Bounds

. . . and whyThese topics help identify and locatethe real zeros of polynomialfunctions.

2.4 REAL ZEROS OF POLYNOMIAL FUNCTIONS

OBJECTIVEStudents will be able to divide polynomi-als using long division or syntheticdivision; to apply the RemainderTheorem, Factor Theorem, and RationalZeros Theorem; and find upper and lowerbounds for zeros of polynomials.

MOTIVATEHave students discuss the vocabulary oflong division: dividend, divisor, quotient,and remainder.

LESSON GUIDEDay 1: Long and Synthetic Division;Reminder and Factor TheoremsDay 2: Rational Zeros; Bounds

Division Algorithm for PolynomialsLet f �x� and d�x� be polynomials with the degree of f greater than orequal to the degree of d, and d�x� � 0. Then there are unique polynomialsq�x� and r �x�, called the and , such that

f �x� � d�x� • q�x� � r �x� (1)

where either r �x� � 0 or the degree of r is less than the degree of d.

remainderquotient

TEACHING NOTEIt is worth emphasizing the fact that thequotient and remainder are unique.Compare the fact that the degree of theremainder must be less than the degreeof the divisor with the correspondingfact for whole number division—theremainder must be less than the divisor.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 47

For instance, in the polynomial division example above we could write

� x2 � x � 2 �

to summarize the relationships between the polynomials being divided andthe resulting quotient and remainder.

EXAMPLE 1 Using polynomial long divisionUse long division to find the quotient and remainder when 2x4 � x3 � 2 isdivided by 2x2 � x � 1. Write a summary statement in both polynomial andfraction form.

SOLUTIONSolve Algebraically

From the division algorithm we know

2x4 � x3 � 2 � �2x2 � x � 1��x2 � x� � �x � 2�.

Using equation (2), we obtain the fraction form

� x2 � x � .

Support GraphicallyIn Figure 2.36 we graph

y � 2x4 � x3 � 2 and

y � �2x2 � x � 1��x2 � x� � �x � 2�

in the same window and see that the graphs appear to be the same.

Remainder and Factor TheoremsAn important special case of the division algorithm occurs when the divisoris of the form d�x� � x � k, where k is a real number. Because the degree ofd�x� � x � k is 1, the remainder is a real number. So we obtain the followingsimplified summary statement for the division algorithm:

f �x� � �x � k�q�x� � r. (3)

We use this special case of the division algorithm throughout the rest of thesection.

Now try Exercise 3.

x � 2��2x2 � x � 1

2x4 � x3 � 2��2x2 � x � 1

x2 � x ← Quotient2x2 � x � 1�2�x�4�� x�3�� 0�x�2�� 0�x�� 2�

2x4 � x3 � x2

�2x3 � x2 � 0x � 2�2x3 � x2 � x

x � 2 ← Remainder

3�3x � 2

3x3 � 5x2 � 8x � 7��

3x � 2


NOTES ON EXAMPLESThe dividend in Example 1 does not havean x2 term or an x term. Students mayneed to be reminded of the importanceof using zero “placeholders” in thissituation.

Figure 2.36 The graphs ofy � 2x4 � x3 � 2 andy � (2x2 � x � 1)(x2 � x) � (x � 2).(Example 1)

[–2, 2] by [–5, 15]

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 48

Using Equation (3), we evaluate the polynomial f �x� at x � k:

f �k� � �k � k�q�k� � r

� 0 • q �k� � r

� 0 � r

� r.

So f �k� � r, which is the remainder. This reasoning gives us the following theorem.

Example 2 shows a clever use of the Remainder Theorem that gives informa-tion about the factors, zeros, and x-intercepts.

EXAMPLE 2 Using the remainder theoremFind the remainder when f �x� � 3x2 � 7x � 20 is divided by

(a) x � 2 (b) x � 1 (c) x � 4.

SOLUTIONSolve Numerically (by hand)(a) We can find the remainder without doing long division! Usingthe Remainder Theorem with k � 2 we find thatr � f �2� � 3�2�2 � 7�2� � 20 � 12 � 14 � 20 � 6.

(b) r � f ��1� � 3��1�22 � 7��1� � 20 � 3 � 7 � 20 � �24.

(c) r � f ��4� � 3��4�2 � 7��4� � 20 � 48 � 28 � 20 � 0.

Interpret Because the remainder in part (c) is 0,x � 4 divides evenlyintof �x� � 3x2 � 7x � 20. So,x � 4 is a factor of f �x� � 3x2 � 7x � 20, �4is a solution of 3x2 � 7x � 20 � 0, and �4 is an x-intercept of the graphof y � 3x2 � 7x � 20. We know all of this without ever dividing, factoring,or graphing!

Support Numerically (using a grapher) We can find the remainders ofseveral division problems at once using the table feature of a grapher.(See Figure 2.37.)

Our interpretation of Example 2c leads us to the following theorem.

Theorem Factor TheoremA polynomial function f �x� has a factor x � k if and only if f �k� � 0.


Theorem Remainder TheoremIf a polynomial f �x� is divided by x � k, then the remainder is r � f �k�.


Figure 2.37 Table for f (x) � 3x2 � 7x � 20 showing theremainders obtained when f (x) is dividedby x � k, for k � �4, �3, . . ., 1, 2.

X

Y1 = 3X^2+7X–20

–4–3–2–1012

0–14–22–24–20–106

Y1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 49

ProofIf f �x� has a factor x � k, then there is a polynomial g�x� such that

f �x� � �x � k�g�x� � �x � k�g�x� � 0.

By the uniqueness condition of the Division Algorithm g�x� is the quotientand 0 is the remainder, and by the Remainder Theorem,f �k� � 0.

Conversely, if f �k� � 0, then the remainder r � 0, and x � k divides evenlyinto f �x� and x � k is a factor of f �x�, with f �x� � �x � k�q�x�.

Applying the ideas of the Factor Theorem and its proof to Example 2,we can factor f �x� � 3x2 � 7x � 20 by dividing it by the known factorx � 4.

So, f �x� � 3x2 � 7x � 20 � �x � 4��3x � 5�. In this case, there really is noneed to use long division, the Remainder Theorem, or the Factor Theorem;traditional factoring methods can do the job. However, when the polynomialfunction involved has degree 3 or higher, these sophisticated methods can bequite helpful in solving equations and finding factors, zeros, and x-intercepts.In fact, the Factor Theorem ties in nicely with earlier connections we havemade in the following way.

Synthetic DivisionWe continue with the important special case of polynomial division thatoccurs when the divisor is of the form x � k. The Remainder Theorem gaveus a way to find remainders in this case without long division. We now learna method for finding both quotients and remainders for division by x � kwithout long division. This shortcut method for the division of a polynomialby a linear divisor x � k is .

We illustrate the evolution of this method below in stages, progressingfrom long division through two intermediate stages to synthetic division.

synthetic division

Fundamental Connections for Polynomial FunctionsFor a polynomial function f and a real number k, the followingstatements are equivalent:

1. x � k is a solution (or root) of the equation f �x� � 0.

2. k is a zero of the function f.

3. k is an x-intercept of the graph of y � f �x�.

4. x � k is a factor of f �x�.

3x � 5x � 4�3�x�2��7�x�� 2�0�

3x2 � 12x�5x � 20�5x � 20

0


TEACHING NOTEStudents may not be used to relation-ships expressed as, “The following state-ments are equivalent….” Note that thismeans any one of the four statementsimplies the other three, and conversely,if any one of the statements is false, soare the others.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 50

Moving from stage to stage, focus on the coefficients and their relative posi-tions. Moving from Stage 1 to Stage 2, we suppress the variable x and thepowers of x, and then from Stage 2 to Stage 3, we eliminate unneeded dupli-cations and collapse vertically.


Stage 3Collapsed Vertically

�3 2 �3 �5 �12 Dividend

�6 �9 �122 3 4 0 Quotient, remainder

Stage 2Variables Suppressed

2 3 4�3�2��3��5��1�2�

2 �63 �5 �123 �9

4 �124 �12

0

Stage 1Long Division

2x2 � 3x � 4x � 3�2�x�3�� 3�x�2�� 5�x�� 1�2�

2x3 � 6x2

3x2 � 5x � 123x2 � 9x

4x � 124x � 12

0

Finally, moving from Stage 3 to Stage 4, we change the sign of the coeffi-cient representing the divisor and the sign of each of the numbers onthe second line of our division scheme. These sign changes yield twoadvantages:

• The number standing for the divisor x � k is now k, its zero.

• Changing the signs in the second line allows us to add rather than subtract.

With Stage 4 we have achieved our goal of synthetic division, a highlystreamlined version of dividing a polynomial by x � k. How does this“bare bones” division work? Example 3 explains the steps.

EXAMPLE 3 Using synthetic divisionDivide 2x3 � 3x2 � 5x � 12 by x � 3 using synthetic division and write asummary statement in fraction form.

SOLUTIONSet UpThe zero of the divisor x � 3 is 3. We write 3 in the divisor position.Because the dividend is in standard form, we write its coefficients in orderin the dividend position, making sure to use a zero as a placeholder for anymissing term. We then prepare for the division process by leaving space forthe line for products and by drawing a horizontal line below the space. (Seebelow.)

Calculate• Because the leading coefficient of the dividend must be the leading

coefficient of the quotient, copy the 2 into the first quotient position.

Stage 4Synthetic Division

Zero of divisor → 3 2 �3 �5 �12 Dividend

6 9 122 3 4 0 Quotient, remainder

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 51

• Multiply the zero of the divisor (3) by the most recently determinedcoefficient of the quotient (2). Write the product above the line and onecolumn to the right.

• Add the next coefficient of the dividend to the product just found andrecord the sum below the line in the same column.

• Repeat the “multiply” and “add” steps until the last row is completed.

InterpretThe last line of numbers are the coefficients of the quotient polynomial andthe remainder. The quotient must be a quadratic function. (Why?) So thequotient is 2x2 � 3x � 4 and the remainder is 0. So we conclude that

� 2x2 � 3x � 4, x � 3.

Rational Zeros TheoremReal zeros of polynomial functions are either —zeros that arerational numbers—or —zeros that are irrational numbers.For example,

f �x� � 4x2 � 9 � �2x � 3��2x � 3�

has the rational zeros �3�2 and 3�2, and

f �x� � x2 � 2 � �x � �2��x � �2��

has the irrational zeros ��2� and �2� .

The Rational Zeros Theorem tells us how to make a list of all potential rational zeros for a polynomial function with integer coefficients.

Theorem Rational Zeros TheoremSuppose f is a polynomial function of degree n 1 of the form

f �x� � anxn � an�1xn�1 � . . . � a0,

with every coefficient an integer and a0 � 0. If x � p�q is a rational zeroof f, where p and q have no common integer factors other than 1, then

• p is an integer factor of the constant coefficient a0, and

• q is an integer factor of the leading coefficient an.

irrational zerosrational zeros

Now try Exercise 7.

2x3 � 3x2 � 5x � 12��

x � 3

Zero of Divisor 3 � 2 �3 �5 �12 DividendLine for products 6 9 12Line for sums 2 3 4 0 Remainder

Quotient

Zero of Divisor 3 2 �3 �5 �12 Dividend

Line for products2


TEACHING NOTEIt is best to see if the coefficients of theterms of f (x) have a common factor thatcan be factored out before applyingthe rational zeros test. Factoring out acommon factor will reduce the numberof extra candidates found.

NOTES ON EXAMPLESHere is a good place to remind studentsthat the function on the left is undefinedfor x � 3. Hence these expressions areonly equal for x values different fromx � 3.

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 52

EXAMPLE 4 Finding the rational zerosFind the rational zeros of f �x� � x3 � 3x2 � 1.

SOLUTION Because the leading and constant coefficients are both 1,according to the Rational Zeros Theorem, the only potential rational zerosof f are 1 and �1. So we check to see if they are in fact zeros of f :

f �1� � �1�3 � 3�1�2 � 1 � �1 � 0

f ��1� � ��1�3 � 3��1�2 � 1 � �3 � 0

So f has no rational zeros. Figure 2.38 shows that the graph of f has threex-intercepts. So f has three real zeros. All three must be irrational numbers.

In Example 4 the Rational Zeros Theorem gave us only two candidates forrational zeros, neither of which “checked out.” Often this theorem suggestsmany candidates, as we see in Example 5. In such a case, we use technologyand a variety of algebraic methods to track down the rational zeros.

EXAMPLE 5 Finding the rational zerosFind the rational zeros of f �x� � 3x3 � 4x2 � 5x � 2.

SOLUTION Because the leading coefficient is 3 and constant coefficient is�2, the Rational Zeros Theorem gives us a list of several potential rationalzeros of f. So we take an organized approach to our solution.

Potential Rational Zeros:

�FFaacctotorsrs

ooff�

32

�: ��

�

11,,

�

�

23

� : �1, �2, ��13

�, ��23

�

Figure 2.39 suggests that, among our candidates, 1,�2, and possibly �1�3 or�2�3 are the most likely to be rational zeros. We use synthetic divisionbecause it tells us whether a number is a zero and, if so, how to factor the poly-nomial. To see whether 1 is a zero off , we synthetically dividef �x� by x � 1:

Zero of Divisor 1 3 4 �5 �2 Dividend

3 7 2

3 7 2 0 Remainder

Quotient

So because the remainder is 0,x � 1 is a factor of f �x� and 1 is a zero of f.By the Division Algorithm and factoring, we conclude

f �x� � 3x3 � 4x2 � 5x � 2

� �x � 1��3x2 � 7x � 2�

� �x � 1��3x � 1��x � 2�

So the rational zeros of f are 1,�1�3, and �2. Now try Exercise 35.



Figure 2.38 The functionf (x) � x3 � 3x2 � 1 has three real zeros.(Example 4)

[–4.7, 4.7] by [–3.1, 3.1]

Figure 2.39 The function f (x) � 3x3 � 4x2 � 5x � 2 has three realzeros. (Example 5)

[–4.7, 4.7] by [–10, 10]

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 53

Upper and Lower BoundsWe narrow our search for real zeros by using a test that identifiesupper and lower bounds for real zeros. A number k is an

of f if f �x� is never zero when x is greater than k. On the otherhand, a number k is a of f if f �x� is neverzero when x is less than k. So if c is a lower bound and d is an upper bound forthe real zeros of a function f, all of the real zeros of f must lie in the intervalc, d�. Figure 2.40 illustrates this situation.

EXAMPLE 6 Establishing bounds for real zerosProve that all of the real zeros of f �x� � 2x4 � 7x3 � 8x2 � 14x � 8 mustlie in the interval �2, 5�.

SOLUTION We must prove that 5 is an upper bound and�2 is a lower boundon the real zeros of f. The function f has a positive leading coefficient, so weemploy the Upper and Lower Bound Test, and use synthetic division:

5 2 �7 �8 14 8

10 15 35 245

2 3 7 49 253 Last line

�2 2 �7 �8 14 8

�4 22 �28 28

2 �11 14 �14 36 Last line

Because the last line in the first division scheme consists of all positive num-bers, 5 is an upper bound. Because the last line in the second division consistsof numbers of alternating signs,�2 is a lower bound. All of the real zeros off must therefore lie in the closed interval �2, 5�.

EXAMPLE 7 Finding the real zeros of a polynomialfunction

Find all of the real zeros of f �x� � 2x4 � 7x3 � 8x2 � 14x � 8.

SOLUTION From Example 6 we know that all of the real zeros of f must liein the closed interval �2, 5�. So in Figure 2.41 we set our Xmin and Xmaxaccordingly.


Upper and Lower Bound Tests for Real ZerosLet f be a polynomial function of degree n 1 with a positive leadingcoefficient. Suppose f �x� is divided by x � k using synthetic division.

• If k 0 and every number in the last line is nonnegative (positive orzero), then k is an upper boundfor the real zeros off .

• If k � 0 and the numbers in the last line are alternately nonnegativeand nonpositive, then k is a lower boundfor the real zeros off .

lower bound for the real zerosthe real zeros

upper bound for


TEACHING NOTEMake certain that students do not con-fuse upper and lower bounds for realzeros of a function with upper andlower bounds for a function’s value.

TEACHING NOTEIt may be helpful to discuss with thestudents the reason the upper boundtest would not apply if the leading coeffi-cient were negative. Also note that sincethe zeros of f are the same as the zerosof �f, the upper and lower bound testsmay be applied to �f if it has a positiveleading coefficient. For example, thezeros of f (x) � �2x3 � x2 can be deter-mined by finding the zeros of g(x) � �f (x) � 2x3 � x2.

Figure 2.40 c is a lower bound and d isan upper bound for the real zeros of f.

y

xc

y � f (x)

d

Figure 2.41 f (x) � 2x4 � 7x3 � 8x2 �

14x � 8 has all of its real zeros in [�2, 5].(Example 7)

[–2, 5] by [–50, 50]

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 54

Next we use the Rational Zeros Theorem.


�FFaaccttoorrss

ooff

82

� :��1, �

�

21,,

�

�

42, �8

� : �1, �2, �4, �8, ��12

�

We compare the x-intercepts of the graph in Figure 2.41 and our list ofcandidates, and decide 4 and �1�2 are the only potential rational zerosworth pursuing.

4 2 �7 �8 14 8

8 4 �16 �8

2 1 �4 �2 0

From this first synthetic division we conclude

f �x� � 2x4 � 7x3 � 8x2 � 14x � 8

� �x � 4��2x3 � x2 � 4x � 2�

and we now divide the cubic factor 2x3 � x2 � 4x � 2 by x � 1�2:

�1�2 2 1 �4 �2

�1 0 2

2 0 �4 0

This second synthetic division allows to complete the factoring off �x�.

f �x� � �x � 4��2x3 � x2 � 4x � 2�

� �x � 4�� x � �12

� ��2x2 � 4�

� 2�x � 4�� x � �12

� ��x2 � 2�

� �x � 4��2x � 1��x � �2��x � �2��

So the zeros of f are the rational numbers 4 and �1�2 and the irrationalnumbers ��2� and �2�.

A polynomial function cannot have more real zeros than its degree, but it canhave fewer. When a polynomial has fewer real zeros than its degree, theUpper and Lower Bounds Test helps us know that we have found them all, asillustrated by Example 8.

EXAMPLE 8 Finding the real zeros of a polynomial functionProve that all of the real zeros off �x� � 10x5 � 3x2 � x � 6 lie in theinterval 0, 1�, and find them.

SOLUTION We first prove that 1 is an upper bound and 0 is a lower boundfor the real zeros of f. The function f has a positive leading coefficient, sowe use synthetic division and the Upper and Lower Bounds Test:



FOLLOW-UPAsk . . .What are two ways one can know thatx � k is a factor of a polynomial f (x)?(Factor and Remainder Theorems)

ASSIGNMENT GUIDEDay 1: Ex. 3–30, multiples of 3, 32, 39,42, 47Day 2: Ex. 33, 36, 51, 54, 57, 58, 60, 62,69, 71, 72, 77COOPERATIVE LEARNINGGroup Activity: Ex. 79NOTES ON EXERCISESEx. 27–32 require students to finda polynomial function with particularzeros or function values.Ex. 37–48 require students to use testsfor upper and lower bound.Ex. 62 encourages students to thinkabout what kind of regression might bemost useful for modeling a particularset of data.Ex. 63–68 provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 5, 7, 33, 35, 45,49, 55Embedded Assessment: Ex. 62, 71

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 55

1 10 0 0 �3 1 �6

10 10 10 7 8

10 10 10 7 8 2 Last line

0 10 0 0 �3 1 �6

0 0 0 0 0

10 0 0 �3 1 �6 . Last line

Because the last line in the first division scheme consists of all positivenumbers, 1 is an upper bound. Because the last line in the second divisionconsists of numbers of alternating signs, 0 is a lower bound. All of the realzeros off must therefore lie in the closed interval 0, 1�. So in Figure 2.42we set our Xmin and Xmax accordingly.

Next we use the Rational Zeros Theorem.


�FFaaccttoorrssooff�

106

� :��

�

11,,�

�

22,,�

�

53,,�

�

160

� :

�1, �2, �3, �6, ��12

�, ��32

�, ��15

�, ��25

�, ��35

�, ��65

�, ��110�, ��

130�.

We compare the x-intercepts of the graph in Figure 2.42 and our list ofcandidates, and decidef has no rational zeros. From Figure 2.42 we see thatf changes sign on the interval 0.8, 1�, so by the Intermediate ValueTheorem must have a real zero on this interval. Because it is not rational weconclude that it is irrational. Figure 2.43 shows that this lone real zero off is approximately 0.95. Now try Exercise 55.


Figure 2.42 y � 10x5 � 3x2 � x � 6.(Example 8)

[0, 1] by [–8, 4]

Figure 2.43 An approximation for theirrational zero of f (x) � 10x5 � 3x2 �

x � 6. (Example 8)

[0, 1] by [–8, 4]

X=.95054589 Y=0Zero

In Exercises 1–4, rewrite the expression as a polynomial instandard form.

1. x2 � 4x � 7 2.

3. 4.

In Exercises 5–10, factor the polynomial into linear factors.

5. x3 � 4x x(x � 2)(x � 2) 6. 6x2 � 54 6(x � 3)(x � 3)

7. 4x2 � 8x � 60 8. 15x3 � 22x2 � 8x

9. x3 � 2x2 � x � 2 10. x4 � x3 � 9x2 � 9x6x4 � 2x3 � 7x2

��3x2

x4 � 3x2 � 7x5

��x2

2x3 � 5x2 � 6x��

2xx3 � 4x2 � 7x��

x

QUICK REVIEW 2.4 (For help, go to Sections A.2. and A.3.)


In Exercises 1–6, divide f �x� by d �x�, and write a summarystatement in polynomial form and fraction form.

1. f �x� � x2 � 2x � 3; d �x� � x � 1

2. f �x� � x3 � 1; d�x� � x � 1

3. f �x� � x3 � 4x2 � 7x � 9; d�x� � x � 3

4. f �x� � 4x3 � 8x2 � 2x � 1; d�x� � 2x � 1

5. f �x� � x4 � 2x3 � 3x2 � 4x � 6; d�x� � x2 � 2x � 1

6. f �x� � x4 � 3x3 � 6x2 � 3x � 5; d�x� � x2 � 1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 56


In Exercises 7–12, divide using synthetic division, and write asummary statement in fraction form.

7.

8.

9. �9x3 �

x �

7x1

2

0� 3x

�

10.

11. �5x4

4�

�

3xx� 1

�

12. �xx

8

�

�

21

�

In Exercises 13–18, use the Remainder Theorem to find theremainder when f �x� is divided by x � k.

13. f �x� � 2x2 � 3x � 1; k � 2 3

14. f �x� � x4 � 5; k � 1 �4

15. f �x� � x3 � x2 � 2x � 1; k � �3 �43

16. f �x� � x3 � 3x � 4; k � �2 2

17. f �x� � 2x3 � 3x2 � 4x � 7; k � 2 5

18. f �x� � x5 � 2x4 � 3x2 � 20x � 3; k � �1 23

In Exercises 19–24, use the Factor Theorem to determinewhether the first polynomial is a factor of the secondpolynomial.

19. x � 1; x3 � x2 � x � 1 20. x � 3; x3 � x2 � x � 15

21. x � 2; x3 � 3x � 4 22. x � 2; x3 � 3x � 2

23. x � 2; 4x3 � 9x2 � 3x � 10

24. x � 1; 2x10 � x9 � x8 � x7 � 2x6 � 3

In Exercises 25 and 26, use the graph to guess possible linearfactors of f �x�. Then completely factor f �x� with the aid ofsynthetic division.

25. f �x� � 5x3 � 7x2 � 49x � 51

26. f �x� � 5x3 � 12x2 � 23x � 42

In Exercises 27–30, find the polynomial function with leadingcoefficient 2 that has the given degree and zeros.

27. Degree 3, with �2, 1, and 4 as zeros

28. Degree 3, with �1, 3, and �5 as zeros

29. Degree 3, with 2,�12

�, and �32

� as zeros

30. Degree 4, with �3, �1, 0, and �52

� as zeros

In Exercises 31 and 32, using only algebraic methods, find thecubic function with the given table of values. Check with agrapher.

31. x �4 0 3 5 f (x) � 3(x � 4)(x � 3)(x � 5)

f �x� 0 180 0 0

32. x �2 �1 1 5 f (x) � 2(x � 2)(x � 1)(x � 5)

f �x� 0 24 0 0

In Exercises 33–36, use the Rational Zeros Theorem to write alist of all potential rational zeros. Then determine which ones, ifany, are zeros.

33. f �x� � 6x3 � 5x � 1 34. f �x� � 3x3 � 7x2 � 6x � 14

35. f �x� � 2x3 � x2 � 9x � 9

36. f �x� � 6x4 � x3 � 6x2 � x � 12

In Exercises 37–40, use synthetic division to prove that thenumber k is an upper bound for the real zeros of the function f.

37. k � 3; f �x� � 2x3 � 4x2 � x � 2

38. k � 5; f �x� � 2x3 � 5x2 � 5x � 1

39. k � 2; f �x� � x4 � x3 � x2 � x � 12

40. k � 3; f �x� � 4x4 � 6x3 � 7x2 � 9x � 2

In Exercises 41–44, use synthetic division to prove that thenumber k is a lower bound for the real zeros of the function f.

41. k � �1; f �x� � 3x3 � 4x2 � x � 3

42. k � �3; f �x� � x3 � 2x2 � 2x � 5

43. k � 0; f �x� � x3 � 4x2 � 7x � 2

44. k � �4; f �x� � 3x3 � x2 � 5x � 3

[–5, 5] by [–75, 75]

[–5, 5] by [–75, 100]

3x4 � x3 � 4x2 � 9x � 3��

x � 5

2x4 � 5x3 � 7x2 � 3x � 1��

x � 3

x3 � 5x2 � 3x � 2��

x � 1

DWFK-PC5-02_v2 01/23/03 9:04 AM Page 57

In Exercises 45– 48, use the upper and lower bound tests todecide whether there is a real zero for the function outside thewindow shown.

45. f �x� � 6x4 � 11x3 � 7x2 � 8x � 34

46. f �x� � x5 � x4 � 21x2 � 19x � 3

47. f �x� � x5 � 4x4 � 129x3 � 396x2 � 8x � 3

48. f �x� � 2x5 � 5x4 � 141x3 � 216x2 � 91x � 25

In Exercises 49–56, find all of the real zeros of the function,finding exact values whenever possible. Identify each zero asrational or irrational.

49. f �x� � 2x3 � 3x2 � 4x � 6

50. f �x� � x3 � 3x2 � 3x � 9

51. f �x� � x3 � x2 � 8x � 6

52. f �x� � x3 � 6x2 � 7x � 4

53. f �x� � x4 � 3x3 � 6x2 � 6x � 8

54. f �x� � x4 � x3 � 7x2 � 5x � 10

55. f �x� � 2x4 � 7x3 � 2x2 � 7x � 4

56. f �x� � 3x4 � 2x3 � 3x2 � x � 2

57. Setting Production Schedules The Sunspot SmallAppliance Co. determines that the supply function for theirEverCurl hair dryer is S� p� � 6 � 0.001p3 and that itsdemand function is D � p� � 80� 0.02p2, where p is theprice. Determine the price for which the supply equals thedemand and the number of hair dryers corresponding to thisequilibrium price. $36.27; 53.7

58. Setting Production Schedules The Pentkon CameraCo. determines that the supply and demand functions fortheir 35 mm�70 mm zoom lens are S� p� � 200� p �0.000007p4 and D � p� � 1500� 0.0004p3, where p is theprice. Determine the price for which the supply equals thedemand and the number of zoom lenses corresponding to thisequilibrium price. $106.99; 1010.15

59. Find the remainder when x40 � 3 is divided by x � 1. �2

60. Find the remainder when x63 � 17 is divided by x � 1. �16

61. Let f �x� � x4 � 2x3 � 11x2 � 13x � 38

(a) Use the upper and lower bound tests to prove that all ofthe real zeros of f lie on the interval �5, 4�. (b) Find all of the rational zeros of f. 2 is a zero of f (x)

(c) Factor f �x� using the rational zero(s) found in (b).

(d) Approximate all of the irrational zeros of f.

(e) Use synthetic division and the irrational zero(s) found in (d) to continue the factorization of f �x� begun in (c).

62. Retail Sales The amount in billions of retail sales by FuelDealers for several years from 1992 to 2000 is given inTable 2.16. Let x � 0 stand for 1990,x � 1 for 1991, andso forth.

(a) Find a quartic regression model, and graph it togetherwith a scatter plot of the data.

(b) Find a quadratic regression model, and graph it togetherwith a scatter plot of the data.

(c) Use the quartic and quadratic regressions from (a)and (b) to get two estimates of the amount of retail sales forFuel Dealers in 2005.

(d) Writing to Learn Give scenarios to justify each of theestimates in (c).

[–5, 5] by [–1000, 1000]

[–5, 5] by [–1000, 1000]

[–5, 5] by [–1000, 1000]

[–5, 5] by [–200, 1000]


DWFK-PC5-02_v2 01/23/03 9:04 AM Page 58

Standardized Test Questions63. True or False The polynomial function f �x� has a factor

x � 2 if and only if f � 2� � 0. Justify your answer.

64. True or False If f �x� � �x � 1��2x2 � x � 1� � 3, then theremainder when f �x� is divided by x � 1 is 3. Justify youranswer.


65. Let f be a polynomial function with f � 3� � 0. Which of thefollowing statements is not true?

(a) x � 3 is a factor of f �x�. (a)

(b) x � 3 is a factor of f �x�.(c) x � 3 is a zero of f �x�.(d) 3 is an x-intercept of f �x�.(e) The remainder when f �x� is divided by x � 3 is zero.

66. Let f �x� � 2x3 � 7x2 � 2x � 3. Which of the following isnot a possible rational root of f ? (e)

(a) �3 (b) �1 (c) 1 (d) 1�2 (e) 2�3

67. Let f �x� � �x � 2��x2 � x � 1� � 3. Which of the followingstatements is not true?(b)

(a) The remainder when f �x� is divided by x � 2 is �3.

(b) The remainder when f �x� is divided by x � 2 is �3.

(c) The remainder when f �x� is divided by x2 � x � 1 is �3.

(d) x � 2 is not a factor of f �x�.(e) f �x� is not evenly divisible by x � 2.

68. Let f �x� � �x2 � 1��x � 2� � 7. Which of the followingstatements is not true?(e)

(a) The remainder when f �x� is divided by x2 � 1 is 7.

(b) The remainder when f �x� is divided by x � 2 is 7.

(c) f � 2� � 7 (d) f � 0� � 5

(e) f does not have a real root.

Explorations69. Archimedes’ Principle A spherical buoy has a radius of

1 m and a density one-fourth that of seawater. ByArchimedes’ Principle, the weight of the displacedwater will equal the weight of the buoy.

• Let x � the depth to which the buoy sinks.

• Let d � the density of seawater.

• Let r � the radius of the circle formed where buoy, air,and water meet. See the figure below.

Notice that 0 x 1 and that

�1 � x�2 � r2 � 1

r2 � 1 � �1 � x�2

� 2x � x2

(a) Verify that the volume of the buoy is 4��3.

(b) Use your result from (a) to establish the weight of thebuoy as �d�3.

(c) Prove the weight of the displaced water is�d • x�3r 2 � x2��6.

(d) Approximate the depth to which the buoy will sink.

70. Archimedes’ Principle Using the scenario of Exercise 63,find the depth to which the buoy will sink if its density isone-fifth that of seawater.� 0.57 m

71. Biological Research Stephanie, a biologist who does researchfor the poultry industry, models the population P of wildturkeys,t days after being left to reproduce, with the function

P�t� � �0.00001t3 � 0.002t2 � 1.5t � 100.

(a) Graph the function y � P�t� for appropriate values of t.

(b) Find what the maximum turkey population is and whenit occurs.

(c) Assuming that this model continues to be accurate, whenwill this turkey population become extinct?

11 � x

x

r

Table 2.16 Fuel Dealers Retail Sales

Year Amount (billions)

1992 19.51994 20.81995 21.61996 24.11997 22.91998 19.71999 20.72000 27.5

Source: U.S. Bureau of the Census, Current BusinessReports, Statistical Abstracts of the United States, 2001.


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 59

(d) Writing to Learn Create a scenario that could explainthe growth exhibited by this turkey population.

72. Architectural Engineering Dave, an engineer at theTrumbauer Group, Inc., an architectural firm, completesstructural specifications for a 172-ft-long steel beam,anchored at one end to a piling 20 ft above the ground. Heknows that when a 200-lb object is placed d feet from theanchored end, the beam bends s feet where

s � �3 � 10�7�d2�550� d�.

(a) What is the independent variable in this polynomialfunction? d

(b) What are the dimensions of a viewing window thatshows a graph for the values that make sense in thisproblem situation?[0, 172] � [0, 5]

(c) How far is the 200-lb object from the anchored end if thevertical deflection is 1.25 ft?� 95.777 ft

73. A classic theorem, , tells us aboutthe number of positive and negative real zeros of a polynomi-al function, by looking at the polynomial’s variations in sign.A variation in signoccurs when consecutive coefficients �instandard form) have opposite signs.

If f �x� � anxn � · · ·� a0 is a polynomial of degree n, then

• The number of positive real zeros of f is equal to the num-ber of variations in sign of f �x�, or that number less someeven number.

• The number of negative real zeros of f is equal to the num-ber of variations in sign of f ��x�, or that number lesssome even number.

Use Descartes’ Rule of Signs to determine the possiblenumbers of positive and negative real zeros of thefunction.

(a) f �x� � x3 � x2 � x � 1

(b) f �x� � x3 � x2 � x � 1

(c) f �x� � 2x3 � x � 3

(d) g�x� � 5x4 � x2 � 3x � 2

Extending the Ideas74. Writing to Learn Graph each side of the Example 3

summary equation:

f �x� � and

g�x� � 2x2 � 3x � 4, x � 3

How are these functions related? Include a discussion of thedomain and continuity of each function.

75. Writing to Learn Explain how to carry out the followingdivision using synthetic division. Work through the stepswith complete explanations.

76. Writing to Learn The figure shows a graph off �x� � x4 � 0.1x3 � 6.5x2 � 7.9x � 2.4. Explain howto use a grapher to justify the statement.

f �x� � x4 � 0.1x3 � 6.5x2 � 7.9x � 2.4

� �x � 3.10��x � 0.5��x � 1.13��x � 1.37�

77. (a) Writing to Learn Write a paragraph that describeshow the zeros of f �x� � �1�3�x3 � x2 � 2x � 3 arerelated to the zeros of g �x� � x3 � 3x2 � 6x � 9. In whatways does this example illustrate how the Rational ZerosTheorem can be applied to find the zeros of a polynomialwith rational number coefficients?

(b) Find the rational zeros of f �x� � x3 � �76

� x2 � �230�x � �

72

�.

(c) Find the rational zeros of f �x� � x3 � �52

� x2 � �3172�x � �

52

�.

78. Use the Rational Zeros Theorem to prove �2� isirrational.

79. Group Activity Work in groups of three.Graph f �x� � x4 � x3 � 8x2 � 2x � 7.

(a) Use grapher methods to find approximate real numberzeros.

(b) Identify a list of four linear factors whose productcould be called an approximate factorization of f�x�.(c) Discuss what graphical and numerical methods youcould use to show that the factorization from (b) isreasonable.

[–5, 5] by [–30, 30]

4x3 � 5x2 � 3x � 1��

2x � 1

2x3 � 3x2 � 5x � 12��

x � 3

Descartes’ Rule of Signs

20 ft

172 ft

d

s


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 60

Complex NumbersFigure 2.44 shows that the function f � x� � x2 � 1 has no real zeros, so x2 � 1 � 0 has no real-number solutions. To remedy this situation, mathe-maticians in the 17th century extended the definition of �a� to include nega-tive real numbers a. First the number i � ��1� is defined as a solution of theequation i2 � 1 � 0 and is the . Then for any negative realnumber �a� � ��a�� • i.

The extended system of numbers, called the complex numbers, consists of allreal numbers and sums of real numbers and real number multiples of i. Thefollowing are all examples of complex numbers:

�6, 5i, �5�, �7i, �52

� i � �23

�, �2 � 3i, 5 � 3i, �13

� � �45

� i.

A real number a is the complex number a � 0i, so all real numbers are alsocomplex numbers. If a � 0 and b � 0, then a � bi becomes bi, and is an

. For instance, 5i and �7i are imaginary numbers.

Two complex numbers are if and only if their real and imaginary partsare equal. For example,

x � yi � 2 � 5i if and only if x � 2 and y � 5.

Operations with Complex NumbersAdding complex numbers is done by adding their real and imaginary partsseparately. Subtracting complex numbers is also done using the same parts.

equal

imaginary number

imaginary unit

SECTION 2.5 Complex Numbers 61

What you’ll learn about■ Complex Numbers■ Operations with Complex Numbers■ Complex Conjugates and Division■ Complex Solutions of Quadratic

Equations■ Complex Plane

. . . and whyThe zeros of polynomials are complexnumbers.

2.5 COMPLEX NUMBERS

Figure 2.44 The graph of f (x) � x 2 � 1has no x-intercepts.

[–5, 5] by [–3, 10]

Definition Complex Number

A is any number that can be written in the form

a � bi,

where a and b are real numbers. The real number a is the ,

the real number b is the , and a � bi is the

.standard formimaginary part

real part

complex number

Definition Addition and Subtraction of Complex Numbers If a � bi and c � di are two complex numbers, then

: �a � bi� � �c � di� � �a � c� � �b � d�i ,

: �a � bi� � �c � di� � �a � c� � �b � d�i .Difference

Sum

Historical Note

René Descartes (1596–1650) coined theterm imaginary in a time when negativesolutions to equations were consideredfalse. Carl Friedrich Gauss (1777–1855)gave us the term complex number andthe symbol i for ��1�. Today practicalapplications of complex numbers abound.

OBJECTIVEStudents will be able to add, subtract,multiply, and divide complex numbers;and find complex zeros of quadraticfunctions.

MOTIVATEAsk . . .If i is the square root of �1, what is thesquare of �i ? (�1)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 61

EXAMPLE 1 Adding and subtracting complex numbers(a) �7 � 3i � � �4 � 5i � � �7 � 4� � ��3 � 5�i � 11 � 2i

(b) �2 � i � � �8 � 3i � � �2 � 8� � ��1 � 3�i � �6 � 4i

The for the complex numbers is 0� 0 � 0i. The

of a � bi is ��a � bi� � �a � bi because

�a � bi� � ��a � bi� � 0 � 0i � 0.

Many of the properties of real numbers also hold for complex numbers.These include:

• Commutative properties of addition and multiplication,

• Associative properties of addition and multiplication, and

• Distributive properties of multiplication over addition and subtraction.

Using these properties and the fact that i 2 � �1, complex numbers can bemultiplied by treating them as algebraic expressions.

EXAMPLE 2 Multiplying complex numbers�2 � 3i � • �5 � i � � 2�5 � i � � 3i �5 � i �

� 10 � 2i � 15i � 3i 2

� 10 � 13i � 3��1�

� 13 � 13i

We can generalize Example 2 as follows:

�a � bi��c � di� � ac � adi � bci � bdi2

� �ac � bd� � �ad � bc�i

Many graphers can perform basic calculations on complex numbers.Figure 2.45 shows how the operations of Examples 1 and 2 look on somegraphers.

We compute positive integer powers of complex numbers by treating them asalgebraic expressions.

EXAMPLE 3 Raising a complex number to a power

If z � �12

� � ��23�� i, find z2 and z3.

SOLUTION

z2 � � �12

� � ��23�� i��

12

� � ��23�� i�

Now try Exercise 9.

inverseadditiveadditive identity

Now try Exercise 3.


TEACHING NOTEThe material in this section is not in theAP Calculus topics syllabi.

TEACHING NOTEIt is useful to compare operations withcomplex numbers to operations withbinomials (i.e., multiply by the FOILmethod), but stress that i is not avariable.

TEACHING NOTEExercise 61 (Powers of i ) could be usedas an in-class exploration beforeaddressing the powers of a moregeneral complex number, as is donein Example 3.

Figure 2.45 Complex number operationson a grapher. (Examples 1 and 2)

(7–3i)+(4+5i)

(2–i)–(8+3i)

(2+3i)*(5–i)

N

11+2i

–6–4i

13+13i

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 62


� �14

� � ��43�� i � �

�43�� i � �

34

� i 2

� �14

� � �2�

43�

� i � �34

� ��1�

� ��12

� � ��23�� i

z3 � z2 • z � ��12

� � ��23�� i��

12

� � ��23�� i�

� ��14

� � ��43�� i � �

�43�� i � �

34

� i 2

� ��14

� � 0i � �34

� ��1�

� �1

Figure 2.46 supports these results numerically.

Example 3 demonstrates that 1�2 � ��3��2�i is a cube root of �1 and a solution of x3 � 1 � 0. In Section 2.6 complex zeros of polynomial functionswill be explored in depth.

Complex Conjugates and DivisionThe product of the complex numbers a � bi and a � bi is a positive real number:

�a � bi� • �a � bi� � a2 � �bi�2 � a2 � b2.

We introduce the following definition to describe this special relationship.

The for the complex numbers is 1� 1 � 0i. The, or , of z � a � bi is

z�1 � �1z

� � �a �

1bi

� � �a �

1bi

� • �aa

�

�

bbii

� � �a2 �

ab2� � �

a2 �

bb2�i.

In general, a quotient of two complex numbers, written in fraction form, canbe simplified as we just simplified 1�z—by multiplying the numerator anddenominator of the fraction by the complex conjugate of the denominator.

EXAMPLE 4 Dividing complex numbersWrite the complex number in standard form.

(a) �3 �

2i

� (b) �25�

�

3ii

�

reciprocalmultiplicative inversemultiplicative identity

Now try Exercise 27.Figure 2.46 The square and cube ofa complex number. (Example 3)

(1/2+i (3)/2)2

(1/2+i–.5+.8660254038i

–1(3)/2)3

Definition Complex Conjugate

The of the complex number z � a � bi is

z� � a��b�i� � a � bi.

complex conjugate

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 63

SOLUTION Multiply the numerator and denominator by the complexconjugate of the denominator.

(a) �3 �

2i

� � �3 �

2i

� • �33

�

�

ii

� (b) �25�

�

3ii

� � �25�

�

3ii

� • �22

�

�

33ii

�

� �362�

�

21i2� �

� �160� � �

120� i � �

7 �

1317i�

� �35

� � �15

� i � �173� � �

1173� i

Complex Solutions of Quadratic EquationsRecall that the solutions of the quadratic equation ax2 � bx � c � 0, wherea, b, and c are real numbers and a � 0, are given by the quadratic formula

x ��b � �

2ab�2�� 4�a�c��.

The radicand b2 � 4ac is the , and tells us whether the solu-tions are real numbers. In particular, if b2 � 4ac 0, the solutions involvethe square root of a negative number and so lead to complex-number solu-tions. In all, there are three cases, which we now summarize:

discriminant


10 � 15i � 2i � 3i 2

��22 � 32

Discriminant of a Quadratic EquationFor a quadratic equation ax2 � bx � c � 0, where a, b, and c are realnumbers and a � 0,

• If b2 � 4ac 0, there are two distinct real solutions.

• If b2 � 4ac � 0, there is one repeated real solution.

• If b2 � 4ac 0, there is a complex conjugate pair of solutions.


NOTES ON EXAMPLESHave the students graph the equationto see that it does not touch or cross thex-axis. Also, have the students calculatethe value of the discriminant and con-firm the prediction that there would bea complex conjugate pair of solutions.

EXAMPLE 5 Solving a quadratic equationSolve x2 � x � 1 � 0.

SOLUTIONSolve AlgebraicallyUsing the quadratic formula with a � b � c � 1, we obtain

x �

��1 �

2��3��

��1� � ��1�2 �� 4�1��1��

2�1�

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 64

� ��12

� � ��23�

� i

So the solutions are �1�2 � ��3��2�i and �1�2 � ��3��2�i, a complexconjugate pair.

Confirm NumericallySubstituting �1�2 � ��3��2�i into the original equation, we obtain

��12

� � ��23�

�i �2

� ��12

� � ��23�

�i � � 1

� ��12

� � ��23�

�i � � ��12

� � ��23�

�i � � 1 � 0

By a similar computation we can confirm the second solution.

Complex PlaneJust as every real number is associated with a point of the real number line,every complex number is associated with a point of the . Thisidea evolved through the works of Caspar Wessel (1745–1818), Jean-RobertArgand (1768–1822), and Gauss (1777–1855). Real numbers are placedalong the horizontal axis and imaginary numbers along the vertical axis. Sothe axes become the and the . The complex num-ber a � bi is located at the point �a, b�. For example, the complex number 2� 3i is associated with the point 2 units to the right and 3 units up from theorigin. (See Figure 2.47.)

Figure 2.47 Plotting points in the complex plane.

EXAMPLE 6 Plotting complex numbersPlot u � 1 � 3i, v � 2 � i, and u � v in the complex plane.

SOLUTION First notice that u � v � �1 � 3i � � �2 � i � � 3 � 2i .The numbers u, v, and u � v are plotted in Figure 2.48.

Figure 2.48 suggests that a quadrilateral formed with two complex numbers,their sum, and the origin as the vertices is a parallelogram. You will be askedto prove this in Exercise 65.


2

(b)

2 + 3i3i

Imaginary axis

Realaxisa

a + bibi

(a)

Imaginary axis

Realaxis

imaginary axisreal axis

complex plane



TEACHING NOTENote that the complex conjugate of 3 is3, and the complex conjugate of 5iis �5i.

FOLLOW-UPDiscuss the similarities and differencesbetween the complex plane and theordinary Cartesian plane.

ASSIGNMENT GUIDEEx. 3–48, multiples of 3, 51, 53, 62, 63, 65,66, 69, 70COOPERATIVE LEARNINGGroup Activity: Ex. 61NOTES ON EXERCISESEx. 1–44 are straightforward computa-tional or graphing exercises relating topowers of i and operations on complexnumbers.Ex. 49–54, 62, require the use of thedistance and/or midpoint formulas.Ex. 55–60 provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 9, 27, 33, 41, 45, 49Embedded Assessment: Ex. 39, 63

Figure 2.48 Two numbers and their sumin the complex plane. (Example 6)

Imaginary axis

RealaxisO

u = 1 + 3i

u + v = 3 + 2i

v = 2 – i

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 65

Some of geometric formulas we studied in the Cartesian plane actuallybecome simpler in the complex plane. For example, the betweenthe points u and v in the complex plane is d � �u � v�, and the ofthe line segment connecting u and v is �u � v��2 (see Exercises 53 and 54).These formulas should remind you of the distance formula and the midpointformula used for points on the (real) number line.

EXAMPLE 7 Using the distance and midpoint formulasFind the distance between u � �4 � i and v � 2 � 5i in the complexplane, and find the midpoint of the segment connecting u and v.

SOLUTION The distance between u and v is given by

�u � v� � ��4 � i � � �2 � 5i �� 6 � 4i �

� ��6��2� �� 4��2� � 2�1�3� � 7.21.

The midpoint of the segment connecting u andv is

�u �

2v

� � � ��2

2� 6i� � �1 � 3i.


��4 � i � � �2 � 5i ��

2

midpointdistance


Figure 2.49 The absolute value ofa complex number.

Imaginary axis

Realaxis

z = a + bibi

a

|z|

In Exercises 1–4, add or subtract, and simplify.

1. �2x � 3� � ��x � 6� x � 9 2. �3y � x� � �2x � y�3. �2a � 4d� � �a � 2d� 4. �6z� 1� � �z� 3� 5z � 4

In Exercises 5–10, multiply and simplify.

5. �x � 3��x � 2� x2 � x � 6

6. �2x � 1��x � 3� 2x2 � 5x � 3

7. �x � �2�� x � �2�� x2 � 2

8. �x � 2�3�� x � 2�3�� x2 � 12

9. x � �1 � �2�� x � �1 � �2�� x2 � 2x � 1

10. x � �2 � �3�� x � �2 � �3�� x2 � 4x � 1

QUICK REVIEW 2.5 (For help, go to Sections A.1 and A.2.)

Solving a Cubic Equation1. Factor x3 � 1, and then solve x3 � 1 � 0. Compare your results

with Example 5. Plot the three solutions in the complex plane. Howare the three points related (compute their distance from the origin)?

2. Factor x3 � 1, and then solve x3 � 1 � 0. Compare your resultswith Example 3. Plot the three solutions in the complex plane.How are the three points related?

EXPLORATION 1

EXPLORATION EXTENSIONSFactor x3 � 27 and then solve x3 � 27 � 0.Plot the solutions in the complex plane.Compute their distance from the origin.Is this the result you expected? (Distanceof all points from origin is 3 units.)

Definition Absolute Value of a Complex NumberThe , or , of the complex number z � a � bi,where a and b are real numbers, is

�z� � �a � bi� � �a�2�� b�2�.

See Figure 2.49.

modulusabsolute value

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 66


In Exercises 1–8, write the sum or difference in the standardform a � bi.

1. �2 � 3i� � �6 � 5i� 8 � 2i 2. �2 � 3i� � �3 � 4i�3. �7 � 3i� � �6 � i� 13 � 4i 4. �2 � i� � �9i � 3� 5 � 8i

5. �2 � i� � �3 � ��3�� 5 � (1 � �3�)i

6. ��5� � 3i� � ��2 � ��9�� 5�� 2

7. �i2 � 3� � �7 � i3� �5 � i

8. ��7� � i2� � �6 � ��8�1�� (�7� � 7) � 9i

In Exercises 9–16, write the product in standard form.

9. �2 � 3i��2 � i� 7 � 4i 10. �2 � i��1 � 3i� 5 � 5i

11. �1 � 4i��3 � 2i� �5 � 14i 12. �5i � 3��2i � 1� �13 � i

13. �7i � 3��2 � 6i� �48 � 4i 14. ��4� � i��6 � 5i�15. ��3 � 4i��1 � 2i� 5 � 10i 16. ��2� � 2i��6 � 5i�

In Exercises 17–20, write the expression in the form bi, whereb is a real number.

17. ��1�6� 4i 18. ��2�5� 5i

19. ��3� �3� i 20. ��5� �5�i

In Exercises 21–24, find the real numbers x and y that make theequation true.

21. 2 � 3i � x � yi 22. 3 � yi � x � 7i

23. �5 � 2i� � 7 � x � �3 � yi� x � 1, y � 2

24. �x � 6i� � �3 � i� � �4 � 2yi� x � 7, y � �7/2

In Exercises 25–28, write the complex number in standard form.

25. �3 � 2i�2 5 � 12i 26. �1 � i�3 �2 � 2i

27. ��22�

� � ��22�

� i �4

�1 28. ��23�

� � �12

� i �3

i

In Exercises 29–32, find the product of the complex number andits conjugate.

29. 2 � 3i 13 30. 5 � 6i 61

31. �3 � 4i 25 32. �1 � �2�i 3

In Exercises 33–40, write the expression in standard form.

33. �2 �

1i

� 2/5 � 1/5i 34. �2 �

i

i� �1/5 � 2/5i

35. �22

�

�

i

i� 3/5 � 4/5i 36. �

23�

i

i� 1/3 � 2/3i

37. ��2 �

1i�

�2�i�i�

� 1/2 � 7/2i 38. ��2 �

5i��

�12�

i2i�

�

39. ��1 �

1i

�

��22i

� i�� 7/5 � 1/5i 40. �

�1 �

�1�

�

2�

�

i ��2�

1

i �� i �

�

In Exercises 41–44, match the complex number with one of thepoints labeled a–f.

41. �3 � 4i (f) 42. 5i � 1 (a)

43. 2i � �1 � 3i� (c) 44. �1 � 2i� � �4 � 6i� (d)

In Exercises 45–48, solve the equation.

45. x2 � 2x � 5 � 0 46. 3x2 � x � 2 � 0

47. 4x2 � 6x � 5 � x � 1 48. x2 � x � 11 � 5x � 8

In Exercises 49–52, plot the given points in the complex plane.Draw the line segment connecting them, and find the length andmidpoint of the segment.

49. 2 � 4i, 2 � 4i 50. �3 � 7i, �3 � 7i

51. 1 � 4i, �2 � 6i 52. �5 � i, 3 � 4i

53. Let u � a � bi and v � c � di. Prove that the distancebetween the points u and v is � u � v �.

54. Let u � a � bi and v � c � di. Prove that the midpoint ofthe line segment determined by u and v is �u � v��2.

Standardized Test Questions55. True or False There are no complex numbers z satisfying

z � � z�. Justify your answer.

56. True or False For the complex number i, i � i2 � i3 � i4 � 0.Justify your answer.


57. Which of the following is the standard form for the product�2 � 3i��2 � 3i�? (e)

(a) �5 � 12i (b) 4 � 9i (c) 13 � 3i (d) �5 (e) 13

58. Which of the following is the standard from for the

quotient �1i�? (d)

(a) 1 (b) �1 (c) i (d) �i (e) �1 � i

6

–6

–6 6

f

e

dc

b

a

Imaginary axis

Realaxis


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 67

59. Assume that 2� 3i is a solution of ax2 � bx � c � 0,where a, b, c are real numbers. Which of the following isalso a solution of the equation?

(a) 2 � 3i (b) �2 � 3i (c) �2 � 3i

(d) 3 � 2i (e) �2 �

13i

� (a)

60. Which of the following is the distance between the pointsu � 1 � i and v � 2 � i in the complex plane?

(a) 1 (b) �3� (c) �5� (d) 3

(e) Distance has no meaning in the complex plane.(c)

Explorations61. Group Activity The Powers of i

(a) Simplify the complex numbers i, i 2, . . . ,i 8 by evaluatingeach one.i; �1; �i; 1; i; �1; �i; 1

(b) Simplify the complex numbers i�1, i�2, . . . ,i�8 byevaluating each one.�i; �1; i; 1; �i; �1; i; 1

(c) Evaluate i 0. 1

(d) Writing to Learn Discuss your results from (a)–(c) withthe members of your group, and write a summary statementabout the integer powers of i.

62. Absolute Value of a Complex Number(a) Plot 2� 3i in the complex plane.

(b) Evaluate � 2 � 3i �. �13�(c) Writing to Learn Explain how � 2 � 3i � is related to thedistance between 2� 3i and the origin. They’re equal.

(d) Writing to Learn Repeat (a)–(c) for the complexnumber a � bi, where a and b are any real numbers.

63. The Powers of a Complex Number(a) Selected powers of 1� i are displayed in Table 2.17. Tryto find a pattern in the data, and use it to predict the real andimaginary parts of �1 � i�7 and �1 � i�8.

(b) Plot �1 � i�0, �1 � i�1, . . . ,�1 � i�6 in the complexplane. Try to find a pattern in the arrangement of the points,and use it to predict the locations of �1 � i�7 and �1 � i�8.

(c) Do your answers from (a) and (b) agree?

(d) Compute �1 � i�7 and �1 � i�8, and reconcile your resultsin (a) and (b), if necessary, with the computed values.

64. Writing to Learn Describe the nature of the graph off �x� � ax2 � bx � c when a, b, and c are real numbersand the equation ax2 � bx � c � 0 has nonreal complexsolutions.

Extending the Ideas65. Connecting Algebra and Geometry Verify that 0, 1� 3i,

2 � i, and 3� 2i, shown in Figure 2.48, are the vertices ofa parallelogram. Then prove that for any distinct, nonzerocomplex numbers u and v, the points 0,u, v, and u � v arethe vertices of a parallelogram.

66. Writing to Learn Describe the graphical relationshipbetween a complex number and its complex conjugate.

67. The complex numbers z, 1, and i are plotted in the complexplane. Match the complex numbers 1�z, �z, �1�z, z�, �z�,� z �, �� z �, � z �i with the points labeled a–h.

68. Prove that the difference between a complex number and itsconjugate is a complex number whose real part is 0.

69. Let u � a � bi and v � c � di be complex numbers instandard form. Determine whether each of the following isalways true, and explain why or why not.

(a) �u � v� � �u� � �v�(b) �u � v� � �u� � �v�(c) �u � v� �u� � �v�

70. Let u � a � bi and v � c � di be complex numbers instandard form. Determine whether each of the following isalways true, and explain why or why not.

(a) �u • v� � �u� • �v�

(b) �u • v� �u� • �v�

(c) �u • v� �u� • �v�

Imaginary axis

Realaxis

h

g

f

e

dc

b

a

i z

1

Table 2.17 Powers of 1 � iPower Real Part Imaginary Part

0 1 01 1 12 0 23 �2 24 �4 05 �4 �46 0 �8


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 68

Two Major TheoremsWe have seen that a polynomial function of degree n can have at most n realzeros. We have also seen that a polynomial can have nonreal complex zeros.The Fundamental Theorem of Algebratells us that a polynomial function ofdegree n has n complex zeros (real and nonreal).

The Factor Theorem extends to the complex zeros of a polynomial function.Thus,k is a complex zero of a polynomial if and only if x � k is a factor ofthe polynomial, even if k is not a real number. We combine this fact with theFundamental Theorem of Algebra to obtain the following theorem.

The Fundamental Theorem of Algebra and the Linear Factorization Theoremare existencetheorems. They tell us of the existence of zeros and linear fac-tors, but not how to find them.

One connection is lost going from real zeros to complex zeros. If k is a nonrealcomplex zero of a polynomial function f �x�, then k is notan x-intercept of thegraph of f. The other connections are preserved:

Fundamental Polynomial Connections in the Complex CaseThe following statements about a polynomial functionf are equivalenteven if k is a nonreal complex number:

1. x � k is a solution (or root) of the equationf �x� � 0.

2. k is a zero of the functionf.

3. x � k is a factor off �x�.

Theorem Linear Factorization TheoremIf f (x� is a polynomial function of degree n 0, then f (x� has preciselyn linear factors and

f (x� � a(x � z1�(x � z2� � � � (x � zn�

where a is the leading coefficient of f (x� and z1, z2, . . . ,zn are thecomplex zeros of f (x�. The zi are not necessarily distinct numbers;some may be repeated.

Theorem Fundamental Theorem of AlgebraA polynomial function of degree n 0 has n complex zeros. Some ofthese zeros may be repeated.

SECTION 2.6 Complex Zeros and the Fundamental Theorem of Algebra 69

What you’ll learn about■ Two Major Theorems■ Complex Conjugate Zeros■ Factoring with Real Number

Coefficients

. . . and whyThese topics provide the completestory about the zeros and factorsof polynomials with real numbercoefficients.

2.6 COMPLEX ZEROS AND THE FUNDAMENTAL

THEOREM OF ALGEBRA

OBJECTIVEStudents will be able to factorpolynomials with real coefficients.

MOTIVATEAsk . . .If a polynomial can be factored as aproduct of n linear factors, what is thedegree of the polynomial? (n)

TEACHING NOTEThe material in this section is not in theAP Calculus topics syllabi.

ALERTThe students may not recognize thedifference between the factoring inthis section and the factoring theyhave done in the past. Emphasizethat in this section, the factors arenot required to have real coefficients.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 69

EXAMPLE 1 Exploring fundamental polynomialconnections

Write the polynomial function in standard form, and identify the zeros ofthe function and the x-intercepts of its graph.

(a) f �x� � �x � 2i��x � 2i�

(b) f �x� � �x � 5��x ��2�i ��x � �2�i �

(c) f �x� � �x � 3��x � 3��x � i��x � i�

SOLUTION(a) The quadratic function f �x� � �x � 2i��x � 2i� � x2 � 4 has two zeros:x � 2i and x � �2i. Because the zeros are not real, the graph of f has no x-intercepts.

(b) The cubic function

f �x� � �x � 5��x ��2�i ��x ��2�i �

� �x � 5��x2 � 2�

� x3 � 5x2 � 2x � 10

has three zeros:x � 5, x � �2�i , and x � ��2�i . Of the three, only x � 5 isan x-intercept.

(c) The quartic function

f �x� � �x � 3��x � 3��x � i��x � i�

� �x2 � 6x � 9��x2 � 1�

� x4 � 6x3 � 10x2 � 6x � 9

has four zeros:x � 3, x � 3, x � i, and x � �i. There are only three distinctzeros. The real zero x � 3 is a repeated zero of multiplicity two. Due to thiseven multiplicity, the graph of f touches but does not cross the x-axis at x � 3,the only x-intercept.

Figure 2.50 supports our conclusions regarding x-intercepts.

Complex Conjugate ZerosIn Section 2.5 we saw that, for quadratic equations ax2 � bx � c � 0 withreal coefficients, if the discriminant b2 � 4ac is negative, the solutions area conjugate pair of complex numbers. This relationship generalizes to poly-nomial functions of higher degree in the following way:

Complex Conjugate ZerosSuppose that f � x� is a polynomial function with real coefficients. If a andb are real numbers with b � 0 and a � bi is a zero of f � x�, then its com-plex conjugate a � bi is also a zero of f � x�.

Now try Exercise 3.


Figure 2.50 The graphs of (a) y � x2 � 4,(b) y � x3 � 5x2 � 2x � 10, and (c) y � x4 � 6x3 � 10x2 � 6x � 9.(Example 1)

[–4, 6] by [–10, 30]

(c)

[–4, 6] by [–25, 25]

(b)

[–5, 5] by [–15, 15]

(a)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 70

EXAMPLE 2 Finding a polynomial from given zerosWrite a polynomial function of minimum degree in standard form with realcoefficients whose zeros include �3, 4, and 2� i.

SOLUTION Because �3 and 4 are real zeros,x � 3 and x � 4 must be factors.Because the coefficients are real and 2� i is a zero, 2� i must also be a zero.Therefore,x � �2 � i) and x � �2 � i� must both be factors of f �x�. Thus,

f �x� � �x � 3��x � 4�x � �2 � i��x � �2 � i��

� �x2 � x � 12��x2 � 4x � 5�

� x4 � 5x3 � 3x2 � 43x � 60

is a polynomial of the type we seek. Any nonzero real number multiple off �x� will also be such a polynomial.

EXAMPLE 3 Finding a polynomial from given zerosWrite a polynomial function of minimum degree in standard form withreal coefficients whose zeros include x � 1, x � 1 � 2i, x � 1 � i.

SOLUTION Because the coefficients are real and 1� 2i is a zero, 1� 2imust also be a zero. Therefore,x � �1 � 2i � and x � �1 � 2i � must both befactors off �x�. Likewise, because 1� i is a zero, 1� i must also be a zero.It follows that x � �1 � i � and x � �1 � i � must both be factors of f �x�.Therefore,

f �x� � �x � 1�x � �1 � 2i��x � �1 � 2i��x � �1 � i��x � �1 � i��

� �x � 1��x2 � 2x � 5��x2 � 2x � 2�

� �x3 � 3x2 � 7x � 5��x2 � 2x � 2�

� x5 � 5x4 � 15x3 � 25x2 � 24x � 10

is a polynomial of the type we seek. Any nonzero real number multiple off �x� will also be such a polynomial.

EXAMPLE 4 Factoring a polynomial with complex zerosFind all zeros of f �x� � x5 � 3x4 � 5x3 � 5x2 � 6x � 8, and write f �x� inits linear factorization.


Now try Exercise 7.


What Can Happen If the Coefficients Are Not Real?1. Use substitution to verify that x � 2i and x � �i are zeros of

f � x� � x2 � ix � 2.

2. Use substitution to verify that x � i and x � 1 � i are zeros off � x� � x2 � x � �1 � i�.

3. What conclusions can you draw from parts 1 and 2? Write asummary of your findings.

EXPLORATION 1

EXPLORATION EXTENSIONSIn questions 1 and 2, check to see if thecomplex conjugates of the given zeros arealso zeros. How does the answer relate tothe complex conjugate zeros statementabove? (No, they are not zeros.)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 71

SOLUTION Figure 2.51 suggests that the real zeros of f are x � �2, x � 1,and x � 4.

Using synthetic division we can verify these zeros and show that x2 � 1 isalso a factor of f. So x � i and x � �i are also zeros. Therefore,

f �x� � x5 � 3x4 � 5x3 � 5x2 � 6x � 8

� �x � 2��x � 1��x � 4��x2 � 1�

� �x � 2��x � 1��x � 4��x � i��x � i�.

Synthetic division can be used with complex number divisors in the sameway it is used with real number divisors.

EXAMPLE 5 Finding complex zerosThe complex number z � 1 � 2i is a zero off �x� � 4x4 � 17x2 � 14x � 65. Find the remaining zeros off �x�,and write it in its linear factorization.

SOLUTION We use a synthetic division to show that f �1 � 2i� � 0:

1 � 2i 4 0 17 14 65

4 � 8i �12 � 16i �27 � 26i �65

4 4 � 8i 5 � 16i �13 � 26i 0

Thus 1� 2i is a zero of f �x�. The complex conjugate 1� 2i must also bea zero. We use synthetic division on the quotient found above to find theremaining quadratic factor:

1 � 2i 4 4 � 8i 5 � 16i �13 � 26i

4 � 8i 8 � 16i 13 � 26i

4 8 13 0

Finally, we use the quadratic formula to find the two zeros of4x2 � 8x � 13:

x �

�

�

��1 � �32

� i

Thus the four zeros off �x� are 1� 2i, 1 � 2i, �1 � �3�2�i, and �1 � �3�2�i.Because the leading coefficient off �x� is 4, we obtain

f �x� � 4x � �1 � 2i�� x � �1 � 2i��

� x � ��1 � i � � x � ��1 � i � �.3�2

3�2

�8 � 12i��

8

�8 � ��1�4�4��

8

�8 � �6�4� �� 2�0�8��

8



Figure 2.51 f (x) � x5 � 3x4 � 5x3 �5x2 � 6x � 8 has three real zeros.(Example 4)

[–4.7, 4.7] by [–125, 125]

NOTES ON EXAMPLERemind students that multiplicationdoes not distribute over multiplication.In other words, the 4 is not to be multi-plied by each of the four factors of f(x).

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 72

If we wish to remove fractions in the factors, we can distribute the 4 to get

f �x� � x � �1 � 2i �� x � �1 � 2i �� 2x � ��2 � 3i �� 2x � ��2 � 3i ��.

Factoring with Real Number CoefficientsLet f �x� be a polynomial function with real coefficients. The LinearFactorization Theorem tells us thatf �x� can be factored into the form

f �x� � a�x � z1� �x � z2� � � � �x � zn�,

where zi are complex numbers. Recall, however, that nonreal complex zerosoccur in conjugate pairs. The product of x � �a � bi� and x � �a � bi� is

x � �a � bi�� x � �a � bi�� x2 � �a � bi�x � �a � bi�x� �a � bi� �a � bi�

� x2 � 2ax � �a2 � b2�.

So the quadratic expression x2 � 2ax � �a2 � b2� is a factor off �x�, andits coefficients are real numbers. A quadratic with no real zeros is

. In other words, if we require that the factors ofa polynomial have real coefficients, the factorization can be accomplishedwith linear factors and irreducible quadratic factors.

EXAMPLE 6 Factoring a polynomialWrite f �x� � 3x5 � 2x4 � 6x3 � 4x2 � 24x � 16 as a product of linear andirreducible quadratic factors, each with real coefficients.

SOLUTION The Rational Zeros Theorem provides a list of candidates for therational zeros of f. The graph of f in Figure 2.52 suggests which candidates totry first. Using synthetic division, we find that x � 2�3 is a zero. Thus,

f �x�� x � �23

� � �3x4 � 6x2 � 24�

� �x � �23

� � �3� �x4 � 2x2 � 8�

� �3x � 2� �x2 � 2� �x2 � 4�

� �3x � 2� �x � �2��x � �2��x2 � 4�

Because the zeros of x2 � 4 are complex, any further factorization wouldintroduce nonreal complex coefficients. We have taken the factorization off as far as possible, subject to the condition that each factor has realcoefficients. Now try Exercise 37.

Factors of a Polynomial with Real CoefficientsEvery polynomial function with real coefficients can be written as a productof linear factors and irreducible quadratic factors, each with real coefficients.

irreducible over the reals



Figure 2.52 f (x) � 3x5 � 2x4 � 6x3 �

4x2 � 24x � 16 has three real zeros.(Example 6)

[–3, 3] by [–20, 50]

FOLLOW-UPAsk students if they can think ofanother way to justify the statementthat an odd-degree polynomial functionwith real coefficients has at least onereal zero. Have them think about endbehavior and continuity.

ASSIGNMENT GUIDEEx. 3–36, multiples of 3, 39–44, 46, 57–59,62, 64–66COOPERATIVE LEARNINGGroup Activity: Ex. 66NOTES ON EXERCISESEx. 1–12, and 45–48 require that studentsproduce a polynomial with desiredcharacteristics.Ex. 57–59 require students to use cubicor quadratic regression.Ex. 51–56 provide practice withstandardized texts.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 7, 15, 29, 33, 37Embedded Assessment: Ex. 42, 44

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 73

We have seen that if a polynomial function has real coefficients, then itsnonreal complex zeros occur in conjugate pairs. Because a polynomial of odddegree has an odd number of zeros, it must have at least one zero that is real.This confirms Example 7 of Section 2.3 in light of complex numbers.

The function f �x� � 3x5 � 2x4 � 6x3 � 4x2 � 24x � 16 in Example 6 fits theconditions of this theorem, so we know right away that we are on the righttrack in searching for at least one real zero.

Polynomial Function of Odd DegreeEvery polynomial function of odd degree with real coefficients has atleast one real zero.


In Exercises 1–4, factor the quadratic expression.

1. 2x2 � x � 3 (2x � 3)(x � 1) 2. 6x2 � 13x � 5

3. 10x2 � 3x � 4 4. 9x2 � 6x � 8

In Exercises 5–6, solve the quadratic equation.

5. x2 � 5x � 11 � 0 6. 2x2 � 3x � 7 � 0

In Exercises 7–10, list all potential rational zeros.

7. 3x4 � 5x3 � 3x2 � 7x � 2 �1, �2, �1/3, �2/3

8. 4x5 � 7x2 � x3 � 13x � 3

9. 5x3 � 4x2 � 3x � 4

10. 12x4 � 8x3 � 7x � 1

QUICK REVIEW 2.6 (For help, go to Sections P.5 and 2.4.)


In Exercises 1–4, write the polynomial in standard form, andidentify the zeros of the function and the x-intercepts of its graph.

1. f �x� � �x � 3i��x � 3i�

2. f �x� � �x � 2��x � �3� i��x � �3� i�3. f �x� � �x � 1��x � 1��x � 2i��x � 2i�

4. f �x� � x�x � 1��x � 1 � i��x � 1 � i�

In Exercises 5–12, write a polynomial function of minimumdegree in standard form with real coefficients whose zerosinclude those listed.

5. i and �i x2 � 1 6. 1 � 2i and 1� 2i

7. 1, 3i, and�3i 8. �4, 1� i, and 1� i

9. 2, 3, and i 10. �1, 2, and 1� i

11. 5 and 3� 2i 12. �2 and 1� 2i

In Exercises 13–16, write a polynomial function of minimumdegree in standard form with real coefficients whose zeros andtheir multiplicities include those listed.

13. 1 (multiplicity 2), �2 (multiplicity 3)

14. �1 (multiplicity 3), 3 (multiplicity 1) x4 � 6x2 � 8x � 3

15. 2 (multiplicity 2), 3� i (multiplicity 1)

16. �1 (multiplicity 2), �2 � i (multiplicity 1)

In Exercises 17–20, match the polynomial function graph to thegiven zeros and multiplicities.

17. �3 (multiplicity 2), 2 (multiplicity 3) (b)

18. �3 (multiplicity 3), 2 (multiplicity 2) (c)

19. �1 (multiplicity 4), 3 (multiplicity 3) (d)

20. �1 (multiplicity 3), 3 (multiplicity 4) (a)

[–5, 5] by [–150, 150]

(d)

[–5, 5] by [–150, 150]

(c)

[–5, 5] by [–150, 150]

(b)

[–5, 5] by [–150, 150]

(a)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 74


In Exercises 21–26, state how many complex and real zeros thefunction has.

21. f �x� � x2 � 2x � 7 2 complex zeros; none real

22. f �x� � x3 � 3x2 � x � 1 3 complex zeros; all 3 real

23. f �x� � x3 � x � 3 3 complex zeros; 1 real

24. f �x� � x4 � 2x2 � 3x � 4 4 complex zeros; 2 real

25. f �x� � x4 � 5x3 � x2 � 3x � 6 4 complex zeros; 2 real

26. f �x� � x5 � 2x2 � 3x � 6 5 complex zeros; 1 real

In Exercises 27–32, find all of the zeros and write a linearfactorization of the function.

27. f �x� � x3 � 4x � 5

28. f �x� � x3 � 10x2 � 44x � 69

29. f �x� � x4 � x3 � 5x2 � x � 6

30. f �x� � 3x4 � 8x3 � 6x2 � 3x � 2

31. f �x� � 6x4 � 7x3 � x2 � 67x � 105

32. f �x� � 20x4 � 148x3 � 269x2 � 106x � 195

In Exercises 33–36, using the given zero, find all of the zerosand write a linear factorization of f�x�.

33. 1 � i is a zero of f �x� � x4 � 2x3 � x2 � 6x � 6.

34. 4i is a zero of f �x� � x4 � 13x2 � 48.

35. 3 � 2i is a zero of f �x� � x4 � 6x3 � 11x2 � 12x � 26.

36. 1 � 3i is a zero of f �x� � x4 � 2x3 � 5x2 � 10x � 50.

In Exercises 37–42, write the function as a product of linearand irreducible quadratic factors all with real coefficients.

37. f �x� � x3 � x2 � x � 2 (x � 2)(x2 � x � 1)

38. f �x� � x3 � x2 � x � 6 (x � 2)(x2 � x � 3)

39. f �x� � 2x3 � x2 � 2x � 3 (x � 1)(2x2 � x � 3)

40. f �x� � 3x3 � 2x2 � x � 2 (x � 1)(3x2 � x � 2)

41. f �x� � x4 � 3x3 � 3x2 � 3x � 4 (x � 1)(x � 4)(x2 � 1)

42. f �x� � x4 � 2x3 � x2 � 8x � 12 (x � 3)(x � 1)(x2 � 4)

In Exercises 43 and 44, use Archimedes’ principle,which statesthat when a sphere of radius r with density dS is placed in aliquid of density dL � 62.5 lb/ft3, it will sink to a depth h where

�3rh2 � h3�dL � �r 3dS.

Find an approximate value for h if:

43. r � 5 ft and dS � 20 lb/ft3. h � 3.776 ft

44. r � 5 ft and dS � 45 lb/ft3. h � 6.513 ft

In Exercises 45–48, answer yes or no. If yes, include anexample. If no, give a reason.

45. Writing to Learn Is it possible to find a polynomial ofdegree 3 with real number coefficients that has �2 as itsonly real zero?

46. Writing to Learn Is it possible to find a polynomial ofdegree 3 with real coefficients that has 2i as its only nonrealzero?

47. Writing to Learn Is it possible to find a polynomial f �x�of degree 4 with real coefficients that has zeros �3, 1� 2i,and 1� i?

48. Writing to Learn Is it possible to find a polynomial f �x� ofdegree 4 with real coefficients that has zeros 1� 3i and 1 � i?

In Exercises 49 and 50, find the unique polynomial with realcoefficients that meets these conditions.

49. Degree 4; zeros at x � 3, x � �1, and x � 2 � i; f �0� � 30

50. Degree 4; zeros at x � 1 � 2i and x � 1 � i; f �0� � 20

Standardized Test Questions51. True or False There is at least one polynomial with real

coefficients with 1� 2i as its only nonreal zero. Justifyyour answer.

52. True or False A polynomial of degree 3 with realcoefficients must have two nonreal zeros. Justify youranswer.


53. Let z be a nonreal complex number and z� its complexconjugate. Which of the following is not a real number?

(a) z � z� (b) z z� (c) |z�| (d) �|1z�|� (e) z2 (e)

54. Which of the following cannot be the number of real zerosof a polynomial of degree 5 with real coefficients?

(a) 0 (b) 1 (c) 2 (d) 3 (e) 4 (a)

55. Which of the following cannot be the number of nonrealzeros of a polynomial of degree 5 with real coefficients?

(a) 0 (b) 2 (c) 3 (d) 4

(e) None of the above.(c)

56. Assume that 1� 2i is a zero of the polynomial f with real coefficients. Which of the following statements is not true? (e)

(a) x � �1 � 2i� is a factor of f �x�.

(b) x2 � 2x � 5 is a factor of f �x�.

(c) x � �1 � 2i� is a factor of f �x�.

(d) 1 � 2i is a zero off.

(e) The number of nonreal complex zeros of f could be 1.

4�3

��3

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 75


Explorations57. Lewis’s distance D from a motion detector is given by the

data in Table 2.18.

(a) Find a cubic regression model, and graph it together witha scatter plot of the data.

(b) Use the cubic regression model to estimate how farLewis is from the motion detector initially.

(c) Use the cubic regression model to estimate when Lewischanges direction. How far from the motion detector is hewhen he changes direction?

58. Sally’s distance D from a motion detector is given by thedata in Table 2.19.

(a) Find a cubic regression model, and graph it together witha scatter plot of the data.

(b) Describe Sally’s motion.

(c) Use the cubic regression model to estimate when Sallychanges direction. How far is she from the motion detectorwhen she changes direction?

59. Jacob’s distance D from a motion detector is given by thedata in Table 2.20.

(a) Find a quadratic regression model, and graph it togetherwith a scatter plot of the data.

(b) Describe Jacob’s motion.

(c) Use the quadratic regression model to estimate whenJacob changes direction. How far is he from the motiondetector when he changes direction?

60. Group Activity The Square Roots of i Let a and b be realnumbers such that �a � bi�2 � i.

(a) Expand the left-hand side of the given equation.

(b) Think of the right-hand side of the equation as 0� 1i,and separate the real and imaginary parts of the equation toobtain two equations.a2 � b2 � 0; 2ab � 1

(c) Solve for a and b.

(d) Check your answer by substituting them in the originalequation.

(e) What are the two square roots of i ?

61. Verify that the complex number i is a zero of the polynomialf �x� � x3 � ix2 � 2ix � 2.

62. Verify that the complex number �2i is a zero of thepolynomial f �x� � x3 � �2 � i�x2 � �2 � 2i�x � 4.

Extending the IdeasIn Exercises 63–64, verify that g�x� is a factor of f �x�. Then findh�x� so that f � g • h.

63. g�x� � x � i ; f �x� � x3 � �3 � i �x2 � 4ix � 1

64. g�x� � x � 1 � i ; f �x� � x3 � �1 � i �x2 � x � 1 � i

65. Connecting Algebra and Geometry In Exercise 65 ofSection 2.5 we proved that 0, 1� 3i, 2 � i, and 3� 2i,shown in Figure 2.48, are the vertices of a parallelogram.Which other points in the complex plane complete a paral-lelogram with 1� 3i, 2 � i, and 3� 2i ?

66. Find the three cube roots of 8 by solving x3 � 8.

67. Find the three cube roots of �64 by solving x3 � �64.

Table 2.20 Motion Detector Data

for Exercise 59

t (sec) D (m) t (sec) D (m)

0.0 4.59 4.5 1.700.5 3.92 5.0 2.251.0 3.14 5.5 2.841.5 2.41 6.0 3.392.0 1.73 6.5 4.022.5 1.21 7.0 4.543.0 0.90 7.5 5.043.5 0.99 8.0 5.594.0 1.31


for Exercise 58


0.0 3.36 4.5 3.590.5 2.61 5.0 4.151.0 1.86 5.5 3.991.5 1.27 6.0 3.372.0 0.91 6.5 2.582.5 1.14 7.0 1.933.0 1.69 7.5 1.253.5 2.37 8.0 0.674.0 3.01


for Exercise 57


0.0 1.00 4.5 0.990.5 1.46 5.0 0.841.0 1.99 5.5 1.281.5 2.57 6.0 1.872.0 3.02 6.5 2.582.5 3.34 7.0 3.233.0 2.91 7.5 3.783.5 2.31 8.0 4.404.0 1.57

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 76

Rational FunctionsRational functions are ratios (or quotients) of polynomial functions.

SECTION 2.7 Rational Functions 77

What you’ll learn about■ Rational Functions■ Transformations of the Reciprocal

Function■ Limits and Asymptotes■ Analyzing Graphs of Rational

Functions

. . . and whyRational functions are used incalculus and in scientificapplications such as Kepler’s Law.

2.7 GRAPHS OF RATIONAL FUNCTIONS

Definition Rational FunctionsLet f and g be polynomial functions with g�x� � 0. Then the functiongiven by

y�x� � �g

f(

(

x

x

)

)�

is a .rational function

OBJECTIVEStudents will be able to describe thegraphs of rational functions, identifyhorizontal and vertical asymptotes, andpredict the end behavior of rationalfunctions.

MOTIVATEAsk students to predict some of thecharacteristics of the graph of y � (x � 2)�(x � 2) and to check theirpredictions with a grapher.

LESSON GUIDEDay 1: Rational Functions;Transformations; Limits and AsymptotesDay 2: Analyzing Graphs

The domain of a rational function is the set of all real numbers except the zerosof its denominator. Every rational function is continuous on its domain.

EXAMPLE 1 Finding the domain of a rational functionFind the domain of f and use limits to describe its behavior at value(s) of xnot in its domain.

f �x� � �x�

12

�

SOLUTION The domain of f is all real numbers x � 2. The graph inFigure 2.53 strongly suggests that f has a vertical asymptote at x � 2.As x approaches 2 from the left, the values of f decrease without bound. Asx approaches 2 from the right, the values of f increase without bound. Usingthe notation introduced in Section 1.2 on page XXX we write

limx→2�

f �x� � �∞ and limx→2�

f �x� � ∞.

The tables in Figure 2.54 support this visual evidence numerically.

Figure 2.54 Table of values for f(x) � 1�(x � 2) for values of x (a) to the right of 2,and (b) to the left of 2. (Example 1)

X

Y1 = 1/(X–2)

22.012.022.032.042.052.06

ERROR1005033.333252016.667

Y1

(a)

X

Y1 = 1/(X–2)

21.991.981.971.961.951.94

ERROR–100–50–33.33–25–20–16.67

Y1

(b)

Now try Exercise 1.

Figure 2.53 The graph of f(x) � 1�(x � 2).(Example 1)

[–4.7, 4.7] by [–5, 5]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 77

In Chapter 1 we defined horizontal and vertical asymptotes of the graph of afunction y � f �x�. The line y � b is a horizontal asymptoteof the graph of f if

limx→�∞

f �x� � b or limx→∞

f �x� � b.

The line x � a is a vertical asymptote of the graph of f if

limx→a�

f �x� � �∞ or limx→a�

f �x� � �∞.

We can see from Figure 2.53 that limx→�∞

1��x � 2� � limx→∞

1��x � 2� � 0 so the

horizontal line y � 0 is a horizontal asymptote of the graph of f �x� � 1��x � 2�.In Example 1 we showed that lim

x→2�f �x� � �∞, and lim

x→2�f �x� � ∞, so the

vertical line x � 2 is a vertical asymptote of f �x� � 1��x � 2�.

Transformations of the Reciprocal FunctionOne of the simplest rational functions is the reciprocal function

f �x� � �1x

�,

which is one of the basic functions introduced in Chapter 1. It can be used togenerate many other rational functions.

Here is what we know about the reciprocal function.


Comparing Graphs of Rational Functions1. Sketch the graph and find an equation for the function g whose

graph is obtained from the reciprocal function f �x� � 1�x by atranslation of 2 units to the right.

2. Sketch the graph and find an equation for the function h whosegraph is obtained from the reciprocal function f �x� � 1�x by a trans-lation of 5 units to the right, followed by a reflection across the axis.

3. Sketch the graph and find an equation for the function k whose graphis obtained from the reciprocal function f �x� � 1�x by a translationof 4 units to the left, followed by a vertical stretch by a factor of 3,and finally a translation 2 units down.

EXPLORATION 1

EXPLORATION EXTENSIONSHave the students use graphers to

graph f (x) � �x1� � 1, f (x) � �x

1� � 2,

f (x) � �x �1

1�, and f (x) � �x �1

2�. Discuss

the results in the shift of the graph of

f (x) � �x1�.

BASIC FUNCTIONS The Reciprocal Functionf �x� � �

1x

�

Domain:�–∞, 0��0, ∞�Range:�–∞, 0��0, ∞�Continuity: All x � 0Decreasing on �–∞, 0� and �0, ∞�Symmetric with respect to origin (an odd function)UnboundedNo local extremaHorizontal asymptotes:y � 0Vertical asymptotes:x � 0End behavior: lim

x→�∞f �x� � lim

x→∞f �x� � 0Figure 2.55 The graph of f (x) � 1�x.

[–4.7, 4.7] by [–3.1, 3.1]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 78

The graph of any rational function of the form

g�x� � �acxx

��

db

�

can be obtained through transformations of the graph of the reciprocal func-tion as illustrated in Example 2. If the degree of the numerator is greater thanor equal to the degree of the denominator, we can use polynomial division torewrite the rational function.

EXAMPLE 2 Transforming the reciprocal functionDescribe how the graph of the given function can be obtained by transformingthe graph of the reciprocal function f �x� � 1�x. Identify the horizontal andvertical asymptotes and use limits to describe the corresponding behavior.Sketch the graph of the function.

(a) g�x� � �x �

23

� (b) h�x� � �3xx��

27

�

SOLUTION

(a) g�x� � �x �

23

� � 2 ��x �

13

� � � 2 f �x � 3�

The graph of g is the graph of the reciprocal function shifted left 3 units

and then stretched vertically by a factor of 2. So the lines x � �3 and

y � 0 are vertical and horizontal asymptotes, respectively. Using limits we

have limx→∞

g�x� � limx→�∞

g�x� � 0, limx→�3�

g�x� � ∞, and limx→�3�

g�x� � �∞.

The graph is shown in Figure 2.56a.

(b) We begin with polynomial division:

3x � 2�3x � 7

3x � 6�1

So,h�x� � �3xx�

�

27

� � 3 � �x �

12

� � �f �x � 2� � 3.

Thus the graph of h is the graph of the reciprocal function translated 2 units

to the right, followed by a reflection across the x-axis, and then translated

3 units up. (Note that the reflection must be executed before the vertical

translation.) So the lines x � 2 and y � 3 are vertical and horizontal

asymptotes, respectively. Using limits we have limx→∞

h�x� � limx→�∞

h�x� � 3,

limx→2�

g�x� � �∞, and limx→2�

g�x� � ∞. The graph is shown in Figure 2.56b.Now try Exercise 9.

SECTION 2.7 Graphs of Rational Functions 79

TEACHING NOTEIf possible, have students compare thegraphs of rational functions using boththe dot mode and the connected modeof a grapher. In the connected mode,students may think that the grapher ispurposely displaying the vertical asymp-totes of the function. The asymptotesthat appear on the grapher are actuallyartifacts of the algorithm used to createthe graphical image on the screen. InExample 2a, for example, the asymptoteshown might be a result of connectingpoints such as (�3.05, �40) and (�2.95,40). If a column of pixels corresponds toexactly x � �3, the grapher finds thatthe function is undefined at that value,so the value is skipped and the asymp-tote does not appear.

Figure 2.56 The graphsof (a) g(x) � 2�(x � 3) and(b) h(x) � (3x � 7)�(x � 2),with their asymptotes overlaid.

y

b)

108642

–4–2

–6–8

–10

–4 –2x

4 6 8 10

y

(a)

108642

–4–2

–6–8

–10

–10–8 –6 –4 –2x

42

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 79

Limits and AsymptotesIn Example 2 we found asymptotes by translating the known asymptotes of thereciprocal function. In Example 3, we use algebra to find an asymptote.

EXAMPLE 3 Finding asymptotesFind the horizontal and vertical asymptotes of f �x� � �x2 � 2��x2 � 1�.Use limits to describe the corresponding behavior of f.

SOLUTIONSolve GraphicallyThe graph off in Figure 2.57 suggests that

limx→∞


f �x� � 1

and that there are no vertical asymptotes. The horizontal asymptote is y � 1.

Figure 2.57 The graph of f (x) � (x2 � 2)�(x2 � 1) with its horizontalasymptote y � 1.

Solve AlgebraicallyThe domain of f is all real numbers. So there are no vertical asymptotes.Using polynomial long division, we find that

f �x� � �xx

2

2��

21

� � 1 � �x2 �

11

�.

When the value of �x� is large, the denominator x2 � 1 is a large positivenumber, and 1��x2 � 1� is a small positive number, getting closer to zeroas �x� increases. Therefore,

limx→∞


f �x� � 1,

so y � 1 is indeed a horizontal asymptote.

Example 3 shows the connection between the end behavior of a rationalfunction and its horizontal asymptote. We now generalize this relationshipand summarize other features of the graph of a rational function:


[–5, 5] by [–1, 3]


TEACHING NOTETo help students intuitively understandthe concept of limit, have them calcu-late and tabulate the decimal valuesof 1�2, 1�3, 1�5, 1�10, 1�100, 1�1000, and1�1,000,000, then discuss what the valueof 1�x “approaches” as x → ∞.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 80

It is a good idea to find all of the asymptotes and intercepts when graphing arational function. If the end behavior asymptote of a rational function is aslant line, we call it a , as illustrated in Example 4.

EXAMPLE 4 Graphing a rational functionFind the asymptotes and intercepts of the function f �x� � x3��x2 � 9� andgraph the function.

SOLUTION The degree of the numerator is greater than the degree of thedenominator, so the end behavior asymptote is the quotient polynomial.Using polynomial long division, we obtain

f �x� � �x2

x�

3

9� � x � �

x29�x

9�.

So the quotient polynomial is q�x� � x, a slant asymptote. Factoring thedenominator,

x2 � 9 � �x � 3��x � 3�,

shows that the zeros of the denominator are x � 3 and x � �3.Consequently,x � 3 and x � �3 are the vertical asymptotes of f. The onlyzero of the numerator is 0, so f �0� � 0, and thus we see that the point �0, 0�is the only x-intercept and the y-intercept of the graph of f.

The graph of f in Figure 2.58a passes through �0, 0� and suggests the verti-cal asymptotes x � 3 and x � �3 and the slant asymptote y � q�x� � x.Figure 2.58b shows the graph of f with its asymptotes overlaid.


slant asymptote


Graphical Features of a Rational Functiony � f (x)�g(x) � (anxn � � � �)�(bMxM � � � �)1. :

If n m, the end behavior asymptote is the horizontal asymptotey � 0.

If n � m, the end behavior asymptote is the horizontal asymptotey � an �bm.

If n m, the end behavior asymptote is the quotient polynomial func-tion y � q�x�, where f �x� � g�x�q�x� � r�x�. There is no horizontalasymptote.

2. : These occur at the zeros of the denominator,provided that the zeros are not also zeros of the numerator of equalor greater multiplicity.

3. : These occur at the zeros of the numerator, which arenot also zeros of the denominator.

4. : This is the value off �0�, if defined.y-intercept

x-intercepts

Vertical asymptotes

End behavior asymptote

Figure 2.58 The graph off (x) � x3�(x2 � 9) (a) by itself and (b) withits asymptotes.

[–9.4, 9.4] by [–15, 15]

(b)

[–9.4, 9.4] by [–15, 15]

(a)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 81

Analyzing Graphs of Rational FunctionsBecause the degree of the polynomial in the numerator of the rational functionin Example 5 is less than the degree of the polynomial in the denominator, weknow that the graph of the function has y � 0 as a horizontal asymptote.

EXAMPLE 5 Analyzing the graph of a rational functionFind the intercepts, asymptotes, use limits to describe the behavior at thevertical asymptotes, and analyze and draw the graph of the rationalfunction

f �x� � �x2 �

x �x �

16

�.

SOLUTION

The numerator is zero when x � 1, so the x-intercept is 1. Because f �0� � 1�6, the y-intercept is 1�6. The denominator factors as

x2 � x � 6 � �x � 3��x � 2�,

so there are vertical asymptotes at x � �2 and x � 3. From the commentspreceding this example we know that the horizontal asymptote is y � 0.Figure 2.59 supports this information and allows us to conclude that

limx→ −2�

f �x� � �∞, limx→ −2�

f �x� � ∞, limx→3�

f �x� � �∞, and limx→3�

f �x� � ∞.

Domain:��∞, �2��2, 3��3, ∞�Range: All realsContinuity: All x � �2, 3Decreasing on ��∞, �2��2, 3��3, ∞�Not symmetricUnboundedNo local extremaHorizontal asymptotes:y � 0Vertical asymptotes:x � �2, x � 3End behavior: lim

x→�∞f �x� � lim

x→∞f �x� � 0

The degrees of the polynomials in the numerator and denominator of the rationalfunction in Example 6 are equal. Thus, we know that the graph of the functionhas y � 2, the quotient of the leading coefficients of the polynomials, as ahorizontal asymptote.

EXAMPLE 6 Analyzing the graph of a rational functionFind the intercepts and analyze and draw the graph of the rational function

f �x� � �2xx2

2

�

�

42

�.

SOLUTION The numerator factors as

2x2 � 2 � 2�x2 � 1� � 2�x � 1��x � 1�,



Figure 2.59 The graph off (x) � (x � 1)�(x2 � x � 6). (Example 5)

[–4.7, 4.7] by [–4, 4]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 82

so the x-intercepts are �1 and 1. The y-intercept is f �0� � 1�2. The denom-inator also factors as

x2 � 4 � �x � 2��x � 2�,

so the vertical asymptotes are x � �2 and x � 2. From the commentspreceding Example 6 we know that y � 2 is the horizontal asymptote.Figure 2.60 supports this information and allows us to conclude that

limx→−2�

f �x� � ∞, limx→−2�

f �x� � �∞, limx→2�

f �x� � �∞, limx→2�

f �x� � ∞.

Domain:��∞, �2��2, 2��2, ∞�Range:��∞, 1�2��2, ∞�Continuity: All x � �2, 2Increasing on ��∞, �2��2, 0�; decreasing on �0, 2��2, ∞�Symmetric with respect to the y-axis (an even function)UnboundedLocal maximum of 1�2 at x � 0Horizontal asymptotes:y � 2Vertical asymptotes:x � �2, x � 2End behavior: lim

x→−∞f �x� � lim

x→∞f �x� � 2

In Examples 7 and 8 we will investigate the rational function

f �x� ��x3 � 3x

x

2

��

13x � 1

�.

The degree of the numerator of f exceeds the degree of the denominator by 2.Thus, there is no horizontal asymptote. We will see that the end behaviorasymptote is a polynomial of degree 2.

EXAMPLE 7 Finding an end behavior asymptoteFind the end behavior asymptote of

f �x� ��x3 � 3x

x

2

��

13x � 1

�

and graph it together with f in two windows:

(a) one showing the details around the vertical asymptote of f,

(b) one showing a graph of f that resembles its end behavior asymptote.

SOLUTION The graph of f has a vertical asymptote at x � 1. Dividex3 � 3x2 � 3x � 1 by x � 1 to show that

f �x� ��x3 � 3x

x

2

��

13x � 1

�� x2 � 2x � 1 � �x �

21

�.

The end behavior asymptote of f is y � x2 � 2x � 1.

(a) The graph of f in Figure 2.61 shows the details around the verticalasymptote. We have also overlaid the graph of its end behavior asymptote.



Figure 2.60 The graph of f (x) � (2x2 � 2)�(x2 � 4). It can be shownthat f takes on no value between 1�2, they-intercept, and 2, the horizontal asymptote.(Example 6)

[–4.7, 4.7] by [–8, 8]

Figure 2.61 The graph of f (x) � (x3 � 3x2 � 3x � 1)�(x � 1) and itsend behavior asymptote y � x2 � 2x � 1.Notice the similarity in the two graphs if weignore the part of the graph of f near thevertical asymptote x � 1.

[–4.7, 4.7] by [–8, 8]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 83

Figure 2.62 The graphs of f (x) � (x3 � 3x2 � 3x � 1)�(x � 1) and its endbehavior asymptote y � x2 � 2x � 1 appear to be identical. (Example 7)

(b) If we draw the graph of f �x� � �x3 � 3x2 � 3x � 1��x � 1� and its endbehavior asymptote y � x2 � 2x � 1 in a large enough viewing windowthe two graphs will appear to be identical. See Figure 2.62.

EXAMPLE 8 Analyzing the graph of a rational functionFind the intercepts and analyze and draw the graph of the rational function

f �x� ��x3 � 3x

x

2

��

13x � 1

�.

SOLUTIONf has only one x-intercept and we can use the graph of f in Figure 2.61 toshow that it is about �0.26. The y-intercept is f �0� � �1. The verticalasymptote is x � 1 as we have seen. We know that the graph of f does nothave a horizontal asymptote, and from Example 7 we know that the endbehavior asymptote is y � x2 � 2x � 1. We can also use Figure 2.61 to showthat f has a local minimum of 3 at x � 2. Figure 2.61 supports this infor-mation and allows us to conclude that

limx→1�

f �x� � �∞ and limx→1�

f �x� � ∞.

Domain: All x � 1Range: All realsContinuity: All x � 1Decreasing on ��∞, 1��1, 2�; increasing on �2, ∞�Not symmetricUnboundedLocal minimum of 3 at x � 2No horizontal asymptotes; end behavior asymptote:y � x2 � 2x � 1Vertical asymptote:x � 1End behavior: lim

x→−∞f �x� � lim

x→∞f �x� � ∞ Now try Exercise 55.


[–40, 40] by [–500, 500]


FOLLOW-UPAsk students how one can tell whetheror not a rational function has a slantasymptote without doing any division.(There is a slant asymptote if the degreeof the numerator minus the degree ofthe denominator is one.)

ASSIGNMENT GUIDEDay 1: Ex. 3–36, multiples of 3Day 2: Ex. 39–60, multiples of 3; 71, 72, 74,75COOPERATIVE LEARNINGGroup Activity: Ex. 69–70NOTES ON EXERCISESEx. 1–22, 37–44 give students practice inevaluating limits.Ex. 63–68, provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 1, 9, 19, 29, 37, 41, 47, 55Embedded Assessment: Ex. 44, 72

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 84


PROBLEM: Given saturated vapor pressures ranging from 12.26 to 65.43millibars, and a constant vapor pressure of 12.26 millibars, what range ofrelative humidity is possible? Does relative humidity increase or decreasewith increasing saturated vapor pressure?

SOLUTION: Given a constant vapor pressure of 12.26, and the followingsaturated vapor pressures, we can compute relative humidity. (Saturatedvapor pressure of 12.26 millibars corresponds to air temperature of about50 degrees Fahrenheit, and saturated vapor pressure of 65.43 millibarscorresponds to air temperature of about 100 degrees Fahrenheit.)

When the saturated vapor pressure is 12.26, the relative humidity isRH� 12.26�SVP� 100 � 12.26�12.26 � 100 � 100%. Similarly, we cancompute the relative humidity for the other values of saturated vaporpressure:

So the relative humidity for these saturated vapor pressures ranges from18.7% to 100%, and we see that relative humidity decreases as saturatedvapor pressure (i.e., temperature) increases.

Saturated Vapor Pressure Relative Humidity (%)

12.26 12.26�12.26 � 100 � 10017.65 12.26�17.65 � 100 � 69.525.01 12.26�25.01 � 100 � 4934.94 12.26�34.94 � 100 � 35.148.12 12.26�48.12 � 100 � 25.565.43 12.26�65.43 � 100 � 18.7

Saturated Vapor Pressure

12.2617.6525.0134.9448.1265.43

In Exercises 1–6, use factoring to find the real zerosof the function.

1. f � x� � 2x2 � 5x � 3 2. f � x� � 3x2 � 2x � 8

3. g�x� � x2 � 4 x � �2 4. g�x� � x2 � 1 x � �1

5. h�x� � x3 � 1 x � 1 6. h�x� � x2 � 1

In Exercises 7–10, find the quotient and remainder when f �x�is divided by d�x�.

7. f � x� � 2x � 1, d�x� � x � 3 2; 7

8. f � x� � 4x � 3, d�x� � 2x � 1 2; 5

9. f � x� � 3x � 5, d�x� � x 3; �5

10. f � x� � 5x � 1, d�x� � 2x 5�2; �1

QUICK REVIEW 2.7 (For help, go to Section 2.4.)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 85


In Exercises 1–4, find the domain of the function f. Use limits todescribe the behavior of f at value(s) of x not in its domain.

1. f �x� � �x �

13

� 2. f �x� � �x��

31

�

3. f �x� � �x2

��1

4� 4. f �x� � �

x2 �2

1�

In Exercises 5–10, describe how the graph of the given functioncan be obtained by transforming the graph of the reciprocalfunction g�x� � 1�x. Identify the horizontal and vertical asymp-totes and use limits to describe the corresponding behavior.Sketch the graph of the function.

5. f �x� � �x �

13

� 6. f �x� � � �x �

25

�

7. f �x� � �2xx�

�

31

� 8. f �x� � �3xx�

�

12

�

9. f �x� � �5

x

�

�

2

4

x� 10. f �x� � �

4x�

�

35x

�

In Exercises 11–14, evaluate the limit based on the graph off shown.

11. limx→3�

f �x� ∞ 12. limx→3�

f �x� �∞13. lim

x→∞ f �x� 0 14. lim

x→�∞f �x� 0

In Exercises 15–18, evaluate the limit based on the graph off shown.

15. limx→�3�

f �x� ∞ 16. limx→�3�

f �x� �∞

17. limx→�∞

f �x� 5 18. limx→∞

f �x� 5

In Exercises 19–22, find the horizontal and vertical asymptotesof f � x�. Use limits to describe the corresponding behavior.

19. f �x� � �2xx2

2

��

31

� 20. f �x� � �x2

3�x2

1�

21. f �x� � �2xx2 �

�x1

� 22. f �x� � �xx2 �

�33x

�

In Exercises 23–30, find the asymptotes and intercepts of thefunction, and graph the function.

23. g�x� � �x2 �

x �

2x2� 3

� 24. g�x� � �x2 �

x �

2x2� 3

�

25. h�x� � �x3

2� x� 26. h�x� � �

x3 �

34x

�

27. f �x� � 28. g�x� �

29. f �x� � 30. g�x� �

In Exercises 31–36, match the rational function with its graph.Identify the viewing window and the scale used on each axis.

31. f �x� � �x �

14

� 32. f �x� � � �x �

13

�

33. f �x� � 2 � �x �

31

� 34. f �x� � 1 � �x �

13

�

35. f �x� � �1 � �4 �

1x

� 36. f �x� � 3 � �x �

21

�

(d)(c)

(b)(a)

x2 � 3x � 7��

x � 3x2 � 2x � 3��

x � 2

�3x2 � x � 12��

x2 � 4

2x2 � x � 2��

x2 � 1

[–9.8, 9] by [–5, 15]

[–5.8, 13] by [–3, 3]


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 86


In Exercises 37–44, find the intercepts, asymptotes, use limits todescribe the behavior at the vertical asymptotes, and analyze anddraw the graph of the given rational function.

37. f �x� � �2x2 �

2x � 3� 38. g�x� � �

x2 � 42x � 3�

39. h�x� � �x2 �

x �x �

112

� 40. k�x� � �x2 �

x3�x �

110

�

41. f �x� � �x2

x�

2 �x �

92

� 42. g�x� � �xx2

2

��

2xx��

28

�

43. h�x� � �x2 �

x �2x

2� 3

� 44. k�x� � �x2 �

x �x �

32

�

In Exercises 45–50, find the end behavior asymptote of the givenrational function f and graph it together with f in two windows:

(a) One showing the details around the vertical asymptote(s) of f.

(b) One showing a graph of f that resembles its end behaviorasymptote.

45. f �x� � �x2 �

x �2x

5� 3

� 46. f �x� � �2x2 �

x �2x

3� 3

�

47. f �x� � �x3 �

x �x2

2� 1

� 48. f �x� � �xx

3

��

11

�

49. f �x� � �x4 �

x �2x

2� 1

� 50. f �x� � �xx

5

2��

11

�

In Exercises 51–56, find the intercepts and analyze and draw thegraph of the given rational funciton.

51. f �x� � �3xx2

2

��

42xx��

54

� 52. g�x� � �x2

4�x2

4�x

2�x

8�

53. h�x� � �xx

3

��

21

� 54. k�x� � �xx

3

��

22

�

55. f �x� ��x3 � 2

2xx

2

��

1x � 1

� 56. g�x� ��2x3 � 2

xx�

2 �2

x � 5�

In Exercises 57–62, find the intercepts, asymptotes, endbehavior asymptote, and graph the function together with itsend behavior asymptote.

57. h�x� � �xx

4

��

11

� 58. k�x� ��2x5 �

xx2

2

��

1x � 1

�

59. f �x� � �xx

5

��

21

� 60. g�x� � �xx

5

��

11

�

61. h�x� � �2x3

x�3 �

3x1� 2

� 62. k�x� � �3x3

x�3 �

x1� 4

�

Standardized Test Questions63. True or False A rational function must have a vertical

asymptote. Justify your answer.

64. True or False f �x� � ��x2

x2

�

�

x

4�� is a rational function.

Justify your answer.


65. Let f �x� � �x2

�

�

23x

�. What values of x have to be excluded

from the domain of f.

(a) only 0 (b) only 3 (c) only �3

(d) only 0, 3 (e) only 0,�3 (e)

66. Let g�x� � �x �

23

�. Which of the transformations of f � x� � �2x

�

produce the graph of g? (a)

(a) Translate the graph of f left 3 units.

(b) Translate the graph of f right 3 units.

(c) Translate the graph of f down 3 units.

(d) Translate the graph of f up 3 units.

(e) Vertically stretch the graph of f by a factor of 2.

67. Let f �x� � �x �

x2

5�. Which of the following statements is true

about the graph of f ? (d)

(a) There is no vertical asymptote.

(b) There is a horizontal asymptote but no vertical asymptote.

(c) There is a slant asymptote but no vertical asymptote.

(d) There is a vertical asymptote and a slant asymptote.

(e) There is a vertical and horizontal asymptote.

68. What is the degree of the end behavior asymptote of

f �x� � �xx

4

8��

11

�?

(a) 0 (b) 1 (c) 2 (d) 3 (e) 4 (e)

Explorations69. Group Activity Work in groups of two. Compare the functions

f �x� � �xx

2

��

39

� and g�x� � x � 3.

(a) Are the domains equal?

(b) Does f have a vertical asymptote? Explain.

(c) Explain why the graphs appear to be identical.

(d) Are the functions identical?

(f)(e)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 87

70. Group Activity Explain why the functions are identical ornot. Include the graphs and a comparison of the functions’asymptotes, intercepts, and domain.

(a) f �x� � �x2 �

x �

x �

12

� and g�x� � x � 2

(b) f �x� � �xx

2

�

�

11

� and g�x� � x � 1

(c) f �x� ��x3 �

xx

2

2�

�

1x � 1

� and g�x� � �x �

11

�

(d) f �x� � �x2 �

x �

x �

12

� and g�x� � �x �

12

�

71. Boyle’s Law This ideal gas law states that the volume of anenclosed gas at a fixed temperature varies inversely as thepressure.

(a) Writing to Learn Explain why Boyle’s Law yields botha rational function model and a power function model.

(b) Which power functions are also rational functions?

(c) If the pressure of a 2.59-L sample of nitrogen gas at291�K is 0.866 atm, what would the volume be at a pressureof 0.532 atm if the temperature does not change?4.22 L

72. Light Intensity Aileen and Malachy gathered the data inTable 2.21 using a 75-watt light bulb and a Calculator-Based Laboratory™ (CBL™) with a light-intensity probe.

(a) Draw a scatter plot of the data in Table 2.21.

(b) Find an equation for the data assuming it has the formf �x� � k�x2 for some constant k. Explain your method forchoosing k. k � 5.81(c) Superimpose the regression curve on the scatter plot.

(d) Use the regression model to predict the light intensity atdistances of 2.2 m and 4.4 m.1.20 W�m2; 0.30 W�m2

Extending the IdeasIn Exercises 73–76, graph the function. Express the function asa piecewise-defined function without absolute value, and use theresult to confirm the graph’s asymptotes and interceptsalgebraically.

73. h�x� � ��

2xx�

�

�

32

� 74. h�x� � ��3xx

��

�

53

�

75. f �x� � ��

5x�

� �

3x4

� 76. f �x� � ��2x�

� �

2x1

�

77. Describe how the graph of

f �x� �

can be obtained from the graph of y � 1�x. (Hint: Use longdivision.)

78. Writing to Learn Let f �x� � 1��x � �1�x�� and g�x� � �x3 � x2 � x��x3 � x�. Doesf � g? Support youranswer by making a comparative analysis of all of the featuresof f and g, including asymptotes, intercepts, and domain.

ax � b�cx � d

Table 2.21 Light Intensity Data

for a 75-W Light Bulb

Distance (m) Intensity(W�m2)

1.0 6.091.5 2.512.0 1.562.5 1.083.0 0.74


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 88

Solving Rational EquationsEquations involving rational expressions or fractions (see Appendix A.3) are

. Every rational equation can be written in the form

�gf ��xx��

� � 0,

where f �x� and g�x� are polynomial functions with no common factors. Thezeros of f �x� are the solutions of the equation.

Usually it is not necessary to put a rational equation in the form of f �x��g�x�.To solve an equation involving fractions we begin by finding the LCD (leastcommon denominator) of all the terms of the equation. Then we clear theequation of fractions by multiplying each side of the equation by the LCD.Sometimes the LCD contains variables.

When we multiply or divide an equation by an expression containing vari-ables, the resulting equation may have solutions that are not solutions of theoriginal equation. These are . For this reason we mustcheck each solution of the resulting equation in the original equation.

EXAMPLE 1 Solving by clearing fractions

Solve x � �3x

� � 4.

SOLUTIONSolve algebraicallyThe LCD is x.

x � �3x

� � 4.

x2 � 3 � 4x Multiply by x.

x2 � 4x � 3 � 0 Subtract 4x.

�x � 1��x � 3� � 0 Factor.

x � 1 � 0 or x � 3 � 0 Zero factor property

x � 1 or x � 3

Support Numerically

For x � 1, x � �3x

� � 1 � �31

� � 4

and for x � 3, x � �3x

� � 3 � �33

� � 4.

Each value is a solution of the original equation.Now try Exercise 3.

extraneous solutions

rational equations

SECTION 2.8 Solving Equations in One Variable 89

What you’ll learn about■ Solving Rational Equations■ Extraneous Solutions■ Applications

. . . and whyApplications involving rationalfunctions as models often requirethat an equation involving fractionsbe solved.

2.8 SOLVING EQUATIONS IN ONE VARIABLE

OBJECTIVEStudents will be able to solve equationsinvolving fractions using both algebraicand graphical techniques and identifyextraneous solutions.

MOTIVATEAsk . . .students to suggest ways to solve

�x �3

2� � �3x2�x

1�

algebraically and graphically.

LESSON GUIDEDay 1: Solving Equations; ExtraneousSolutionsDay 2: Applications

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 89

When the fractions in Example 2 are cleared, we obtain a quadratic equation.

EXAMPLE 2 Solving a rational equation

Solve x � �x �

14

� � 0.

SOLUTIONSolve Algebraically The LCD is x � 4.

x � �x �

14

� � 0.

x�x � 4� � �xx

��

44

� � 0 Multiply by x � 4.

x2 � 4x � 1 � 0 Distributive property

x � Quadratic formula

x � �4 �

22�3�� Simplify.

x � 2 � �3� Simplify.

x � 0.268, 3.732

Solve GraphicallyThe graph in Figure 2.63 suggests that the function y � x � 1��x � 4� hastwo zeros. We can use the graph to show that the zeros are about 0.268 and3.732, agreeing with the values found algebraically.

Extraneous SolutionsWe will find extraneous solutions in Examples 3 and 4.

EXAMPLE 3 Eliminating extraneous solutionsSolve the equation

�x

2�

x1

� � �x �

13

� � �x2 � 4

2x � 3�.

SOLUTIONSolve AlgebraicallyThe denominator of the right-hand side,x2 � 4x � 3, factors into�x � 1��x � 3�. So the least common denominator (LCD) of the equationis �x � 1��x � 3�, and we multiply both sides of the equation by this LCD:

�x � 1��x � 3� ��x 2�

x1

� � �x �

13

� � � �x � 1��x � 3� ��x2 � 42x � 3��

2x�x � 3� � �x � 1� � 2 Distributive property

Now try Exercise 7.

4 � �(�4)2�� 4(1)�(1)��

2(1)


TEACHER’S NOTEEncourage students to see if they canidentify the step that causes anextraneous solution to be introduced.Emphasize that extraneous solutionsreaffirm the importance of checkingsolutions.

Figure 2.63 The graph of y � x � 1�(x � 4). (Example 2)

[–5, 8] by [–5, 10]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 90

2x2 � 5x � 3 � 0 Distributive property

�2x � 1��x � 3� � 0 Factor.

x � ��12

� or x � 3

Confirm NumericallyWe replace x by �1�2 in the original equation:

� �?

� �?

The equation is true, so x � �1�2 is a valid solution. The original equationis not defined for x � 3, so x � 3 is an extraneous solution.

Support GraphicallyThe graph of

f �x� � �x

2�x

1� � �

x �

13

� � �x2 � 4

2x � 3�

in Figure 2.64 suggests that x � �1�2 is an x-intercept and x � 3 is not.

InterpretOnly x � �1�2 is a solution.

We will see that Example 4 has no solutions.

EXAMPLE 4 Eliminating extraneous solutionsSolve

�x �

x3

� � �x �

32

� � �x2 �

62x

� � 0.

SOLUTION The LCD is x�x � 2�.

�x �

x3

� � �x �

32

� � �x2 �

62x

� � 0

�x � 3��x � 2� � 3x � 6 � 0 Multiply by x(x�2).

x2 � x � 6 � 3x � 6 � 0 Expand.

x2 � 2x � 0 Simplify.

x�x � 2� � 0 Factor.

x � 0 or x � �2

Substituting x � 0 or x � �2 into the original equation results in divisionby zero. So both of these numbers are extraneous solutions and the originalequation has no solution. Now try Exercise 17.


8�21

2�7

2�3

2��1�2�2 � 4��1�2� � 3

1��1�2� � 3

2��1�2��1�2� � 1


Figure 2.64 The graph of f (x) �

2x�(x � 1) � 1�(x � 3) � 2�(x2 � 4x � 3).(Example 3)

[–4.7, 4.7] by [–10, 10]

TEACHER’S NOTEThe notion of an extraneous solutionprovides an oppurtunity for students toinvestigate the interplay betweengraphical and algebraic representationsof equations. The graph of the equationin Example 4 is very unusual and will bediscussed in more detail in Exercise 51.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 91


Figure 2.66 The graphs of f (x) � (x � 17.5)�(x � 50) and g(x) � 0.75(Example 5)

0

0.2

0.4

0.6

0.8

1.0

40 80mL of acid

Intersection: x = 80; y = .75

Acid Mixture

Con

cent

ratio

n

120 160x

y

Applications

EXAMPLE 5 Calculating acid mixturesHow much pure acid must be added to 50 mL of a 35% acid solution toproduce a mixture that is 75% acid? (See Figure 2.65.)

SOLUTIONModel

Word statement: �mmLL

ooffpmur

iext

aucried

�� concentration of acid

0.35 � 50 or 17.5 � mL of pure acid in 35% solution

x � mL of acid added

x � 17.5 � mL of pure acid in resulting mixture

x � 50 � mL of the resulting mixture

�xx�

�

1570.5

� � concentration of acid

Solve Graphically

�xx�

�

1570.5

� � 0.75 Equation to be solved

Figure 2.66 shows graphs of f �x� � �x � 17.5��x � 50� and g�x� � 0.75.The point of intersection is �80, 0.75�.

InterpretWe need to add 80 mL or more of pure acid to the 35% acid solution tomake a solution that is 75% acid.

EXAMPLE 6 Finding a minimum perimeterFind the dimensions of the rectangle with minimum perimeter if its area is200 square meters. Find this least perimeter.

SOLUTIONModel

Figure 2.67 A rectangle with area 200 m2. (Example 6)

x

200x

200x

A = 200 = x ba


Figure 2.65 Mixing solutions. (Example 5)

Pure acid

50 mL of a 35%acid solution

Figure 2.68 A graph of P(x) � 2x �

400�x. (Example 6)

[0, 50] by [0, 150]

X=14.142136 Y=56.568542Minimum

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 92

Word Statement: Perimeter� 2 � length� 2 � width

x � width in meters

�20x0

� � �wairdetah

� � length in meters

Function to be minimized: P�x� � 2x � 2��20x0

� � � 2x � �40x0

�

Solve GraphicallyThe graph of P in Figure 2.68 shows a minimum of approximately 56.57,occurring when x � 14.14.

InterpretThe width is about 14.14 m, and the minimum perimeter is about 56.57 m.Because 200�14.14� 14.14, the dimensions of the rectangle with minimumperimeter are 14.14 m by 14.14 m, a square.

EXAMPLE 7 Designing a juice canStewart Cannery will package tomato juice in 2-liter cylindrical cans.Find the radius and height of the cans if the cans have a surface area of1000 cm2. (See Figure 2.69.)

SOLUTIONModel

S� surface area of can in cm2

r � radius of can in centimeters

h � height of can in centimeters

Using volume �V� and surface area �S� formulas and the fact that1 L � 1000 cm3, we conclude that

V � �r2h � 2000 and S� 2�r 2 � 2�rh � 1000.

So

2�r 2 � 2�rh � 1000

2�r 2 � 2�r ��2�

0r0

20

� � � 1000 Substitute h � 2000�(�r2).

2�r 2 � �40

r00� � 1000 Equation to be solved

Solve GraphicallyFigure 2.70 shows the graphs of f �x� � 2�r 2 � 4000�r and g�x� � 1000.One point of intersection occurs when r is approximately 9.65. A secondpoint of intersection occurs when r is approximately 4.62.



Figure 2.69 A tomato juice can.(Example 7)

2r

h

Figure 2.70 (Example 7)

[0, 20] by [0, 4000]

X=9.6549296 Y=1000Intersection

ASSIGNMENT GUIDEDay 1: Ex. 1–30 odds, 51Day 2: Ex. 31–44 odds, 53COOPERATIVE LEARNINGGroup Activity: Ex. 36, 38NOTES ON EXERCISESEx. 5, 11–18 provide practice withextraneous solutions.Ex. 9–22 provide practice graphicallywith extraneous solutions.Ex. 43–44 provide practice with real data.Ex. 45–50 provide practice withstandardized tests.

ONGOING ASSESSMENTSelf-Assessment: Ex. 3, 7, 13, 17, 31, 35, 37Embedded Assessment: Ex. 31, 39

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 93


In Exercises 1–6, solve the equation algebraically. Check forextraneous solutions. Support your answer numerically.

1. �x �

32

� � �x �

35

� � �13

� 2. x � 2 � �1x5�

3. x � 5 � �1x4� 4. �

1x

� � �x �

23

� � 4

5. x � �x

4�x

3� � �

x1�2

3� 6. �

x �3

1� � �

2x

� � 8

In Exercises 7–12, solve the equation graphically. Confirm youranswer algebraically and identify any extraneous solutions.

7. x � �1x0� � 7 8. x � 2 � �

1x5�

9. x � �1x2� � 7 10. x � �

6x

� � �7

11. 2 � �x �

11

� � �x2

1� x� 12. 2 � �

x �3

4� � �

x21�2

4x�

In Exercises 13–18, solve the equation algebraically. Check forextraneous solutions. Support your answer graphically.

13. �x

3�x

5� � �

x �1

2� � �

x2 � 37x � 10�

14. �x

4�x

4� � �

x �3

1� � �

x2 �135x � 4�

15. �x �

x3

� � �x �

31

� � �x2

3� x� � 0

16. �x �

x2

� � �x �

41

� � �x2

2� x� � 0

17. �x �

32

� � �x2 �

62x

� � �3 �

xx

�

18. �x �

x3

� � �x �

23

� � �x2 �

63x

�

In Exercises 19–22, two possible solutions to the equation f �x� � 0are listed. Use the given graph of y � f �x� to decide which, if any,are extraneous.

19. x � �5 or x � �2

[–10, 8.8] by [–5, 5]


In Exercises 1 and 2, find the missing numerator or denominator.

1. �x

2�x

3� � �

x2 � x?

� 12� 2. �

xx

��

11

� � �x2 �

?1

�

In Exercises 3–6, find the LCD and rewrite the expression as asingle fraction reduced to lowest terms.

3. �152� � �

178� � �

56

� 4. �x �

31

� � �1x

�

5. �2x

x� 1� � �

x �2

3�

6. �x2 �x �

5x1� 6

� � �x2

3�x �

x �11

6�

In Exercises 7–10, use the quadratic formula to find the zerosof the quadratic polynomials.

7. 2x2 � 3x � 1 8. 2x2 � 5x � 1

9. 3x2 � 2x � 2 10. x2 � 3x � 9

QUICK REVIEW 2.8 (For help, go to Sections A.3. and P.5.)

Because h � 2000��r 2�, the corresponding values for h are

h � ��4.

2601090. . .�2� � 29.83 and h � �

��9.2605040. . .�2� � 6.83.

InterpretWith a surface area of 1000 cm2, the cans either have a radius of 4.62 cmand a height of 29.83 cm or have a radius of 9.65 cm and a height of 6.83 cm. Now try Exercise 37.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 94


20. x � �2 or x � 3

21. x � �2 or x � 2

22. x � 0 or x � 3

In Exercises 23–30, solve the equation.

23. �x �

21

� � x � 5

24. �x2 �

x26�x

2� 5

� � 3

25. �x2 �

x �2x

5� 1

� � 0

26. �x

3�x

2� � �

x �2

1� � �

x2 �5x � 2�

27. �x

4�x

4� � �

x �5

1� � �

x2 �135x � 4�

28. �x

3�x

1� � �

x �5

2� � �

x2 �1x5

� 2�

29. x2 � �5x

� � 8

30. x2 � �3x

� � 7

31. Acid Mixture Suppose that x mL of pure acid are added to125 mL of a 60% acid solution. How many mL of pure acidmust be added to obtain a solution of at least 83% acid?

(a) Explain why the concentration C�x� of the new mixture is

C�x� � .

(b) Suppose the viewing window in the figure is used to finda solution to the problem. What is the equation of the hori-zontal line?y � 0.83

(c) Writing to Learn Write and solve an equation thatanswers the question of this problem. Explain your answer.

32. Acid Mixture Suppose that x mL of pure acid are added to100 mL of a 35% acid solution.

(a) Express the concentration C�x� of the new mixture as afunction of x.

(b) Use a graph to determine how much pure acid should beadded to the 35% solution to produce a new solution that is75% acid.

(c) Solve (b) algebraically.

33. Breaking Even Mid Town Sports Apparel, Inc., has foundthat it needs to sell golf hats for $2.75 each in order to becompetitive. It costs $2.12 to produce each hat, and it hasweekly overhead costs of $3000.

(a) Let x be the number of hats produced each week. Expressthe average cost (including overhead costs) of producing onehat as a function of x.

(b) Solve algebraically to find the number of golf hats thatmust be sold each week to make a profit. Support youranswer graphically.

(c) Writing to Learn How many golf hats must be sold tomake a profit of $1000 in 1 week? Explain your answer.

0

0.2

0.4

0.6

0.8

1.0

50 100mL of acid

Acid Mixture

Con

cent

ratio

n

200150 250x

y

x � 0.6�125��

x � 125

[–4.7, 4.7] by [–5, 5]

[–4.7, 4.7] by [–10, 10]

[–4.7, 4.7] by [–5, 5]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 95

34. Bear Population The number of bears at any time t(in years) in a federal game reserve is given by

P�t� � �51000

�

�

02.550tt

�.

(a) Find the population of bears when the value of t is 10,40, and 100.

(b) Does the graph of the bear population have a horizontalasymptote? If so, what is it? If not, why not?

(c) Writing to Learn According to this model, what is thelargest the bear population can become? Explain youranswer.

35. Minimizing Perimeter Consider all rectangles with anarea of 182 ft2. Let x be the length of one side of such arectangle.

(a) Express the perimeter P as a function of x.

(b) Find the dimensions of the rectangle that has the leastperimeter. What is the least perimeter?

36. Group Activity Page Design Hendrix Publishing Co.wants to design a page that has a 0.75-in. left border, a1.5-in. top border, and borders on the right and bottom of 1-in. They are to surround 40 in.2 of print material. Let x bethe width of the print material.

(a) Express the area of the page as a function of x.

(b) Find the dimensions of the page that has the least area.What is the least area?

37. Industrial Design Drake Cannery will pack peaches in0.5-L cylindrical cans. Let x be the radius of the can in cm.

(a) Express the surface area Sof the can as a function of x.

(b) Find the radius and height of the can if the surface areais 900 cm3.

38. Group Activity Designing a Swimming Pool ThompsonRecreation, Inc., wants to build a rectangular swimmingpool with the top of the pool having surface area 1000 ft2.The pool is required to have a walk of uniform width 2 ftsurrounding it. Let x be the length of one side of the pool.

(a) Express the area of the plot of land needed for the pooland surrounding sidewalk as a function of x.

(b) Find the dimensions of the plot of land that has the leastarea. What is the least area?

39. Resistors The total electrical resistance R of tworesistors connected in parallel with resistances R1

andR2 is given by

�R1

� � �R1

1� � �

R1

2�

One resistor has a resistance of 2.3 ohms. Let x be theresistance of the second resistor.

(a) Express the total resistance R as a function of x.

(b) Find the resistance of the second resistor if the totalresistance of the pair is 1.7 ohms.

40. Designing Rectangles Consider all rectangles with an areaof 200 m2. Let x be the length of one side of such arectangle.

(a) Express the perimeter P as a function of x.

(b) Find the dimensions of a rectangle whose perimeter is70 m.

41. Swimming Pool Drainage Drains A and B are used toempty a swimming pool. Drain A alone can empty the poolin 4.75 h. Let t be time it takes for drain B alone to emptythe pool.

(a) Express as a function of t the part D of the drainagethat can be done in 1 h with both drains open at thesame time.

(b) Find graphically the time it takes for drain B alone toempty the pool if both drains, when open at the same time,can empty the pool in 2.6 h. Confirm algebraically.

42. Time-Rate Problem Josh rode his bike 17 mi from hishome to Columbus, and then traveled 53 mi by car fromColumbus to Dayton. Assume that the average rate of thecar was 43 mph faster than the average rate of the bike.

(a) Express the total time required to complete the 70-mi trip(bike and car) as a function of the rate x of the bike.

(b) Find graphically the rate of the bike if the total time ofthe trip was 1 h 40 min. Confirm algebraically.

43. Fast Food Sales The total amountin sales in billions of dollars by fast food business for several yearsis given in Table 2.22. Let x � 0represent 1990,x � 1 represent1991, and so forth. A model for the data is given by

y � 120� �x5�00

8�

(a) Graph the model together with a scatter plot of the data.

(b) Use the model to estimate the amount of sales by fastfood business in 2005.

0 200

100

200

300

400

500

50 100 150 250Time (years)

Wildlife Population

Num

ber

of b

ears

x

y


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 96

44. Number of Wineries The number of wineries for severalyears is given in Table 2.23. Let x � 0 represent 1970,x � 1,represent 1971, and so forth. A model for this data is given by

y � 3000� �3x9�,50

90

�

(a) Graph the model together with a scatter plot of the data.

(b) Use the model to estimate the number of wineries in 2005.

Standardized Test Questions45. True or False An extraneous solution of a rational equation

is also a solution of the equation. Justify your answer.

46. True or False The equation 1��x2 � 4� � 0 has no solution.Justify your answer.


47. Which of the following are the solutions of the equation

x � �x

3�x

2� � �

x �6

2�? (d)

(a) x � �2 or x � 3

(b) x � �1 or x � 3

(c) only x � �2

(d) only x � 3

(e) There are no solutions.


1 � �3x

� � �x2 �

62x

�? (c)

(a) x � �2 or x � 4

(b) x � �3 or x � 0

(c) x � �3 or x � 4

(d) only x � �3



�x �

x2

� � �x �

25

� � �x2 � 3

1x4

� 10�? (e)

(a) x � �5 or x � 3

(b) x � �2 or x � 5

(c) only x � 3

(d only x � �5


50. Ten liters of a 20% acid solution are mixed with 30 liters ofa 30% acid solution. Which of the following is the percentof acid in the final mixture?

(a) 21% (b) 22.5% (c) 25% (d) 27.5 (e) 28% (d)

Explorations51. Revisit Example 4 Consider the following equation, which

we solved in Example 4.

�x �

x3

� � �x �

32

� � �x2 �

62x

� � 0

Let f �x� � �x �

x3

� � �x �

32

� � �x2 �

62x

�

(a) Combine the fractions in f �x� but do not reduce tolowest terms.

(b) What is the domain of f ?

(c) Write f as a piecewise-defined function.

(d) Writing to Learn Graph f and explain how the graphsupports your answers in (b) and (c).

Extending the IdeasIn Exercises 52–55, solve for x.

52. y � 1 � �1 �

1x

� 53. y � 1 � �1 �

1x

�

54. y � 1 � 55. y � 1 �1

��1 � �

1 �1

x�

1�1 � �

1x

�

Table 2.23 Number of Wineries

Year Number

1975 5791980 9121985 13751990 16251995 18132000 2188

Source: American Vintners Association as reported in USA TODAY on June 28, 2002

Table 2.22 Fast Food Sales

Year Amount (in billions)

1992 70.61993 74.91994 78.51995 82.51996 85.91997 88.81998 92.51999 97.52000 101.42001 105.5

Source: Technomic, as reported in USA Today July 3–4, 2002


DWFK-PC5-02_v2 01/23/03 9:05 AM Page 97


Polynomial InequalitiesEvery polynomial inequality can be written in the form f �x� 0, f �x� 0,f �x� 0, or f �x� � 0, where f �x� is a polynomial. There is a fundamentalconnection between inequalities and the positive or negative sign of thecorresponding expression f �x�:

• To solve the inequality f �x� 0 is to find the values of x that make f �x�positive.

• To solve the inequality f �x� 0 is to find the values of x that make f �x�negative.

If the expression f �x� is a product, we can determine its sign by determiningthe sign of each of its factors. Example 1 illustrates that a polynomialfunction changes sign only at its real zeros of odd multiplicity.

EXAMPLE 1 Finding where a polynomial is zero,positive, or negative

Let f �x� � �x � 3��x2 � 1��x � 4�2. Determine the real number values of xthat cause f �x� to be (a) zero,(b) positive,(c) negative.

SOLUTION We begin by verbalizing our analysis of the problem:

(a) The real zeros of f �x� are �3 (with multiplicity 1) and 4 (withmultiplicity 2). So f �x� is zero if x � �3 or x � 4.

(b) The factor x2 � 1 is positive for all real numbers x. The factor �x � 4�2

is positive for all real numbers x except x � 4, which makes �x � 4�2 � 0.The factor x � 3 is positive if and only if x �3. So f �x� is positive ifx �3 and x � 4.

(c) By process of elimination,f �x� is negative if x �3.

This verbal reasoning process is aided by the following , whichshows the x-axis as a number line with the real zeros displayed as thelocations of potential sign change and the factors displayed with their signvalue in the corresponding interval:

��2 ��2 ��2

Negative Positive Positivex

�3 4

Figure 2.71 supports our findings because the graph of f is above thex-axis for x in ��3, 4� or �4, ∞�, is on the x-axis for x � �3 or x � 4, andis below the x-axis for x in ��∞, �3�.

Our work in Example 1 allows us to report the solutions of four polynomialinequalities:

• The solution of �x � 3��x2 � 1��x � 4�2 0 is ��3, 4� � �4, ∞�.

Now try Exercise 1.

sign chart

What you’ll learn about■ Polynomial Inequalities■ Rational Inequalities■ Other Inequalities■ Applications

. . . and whyDesigning containers as well asother types of applications oftenrequire that an inequality be solved.

2.9 SOLVING INEQUALITIES IN ONE VARIABLE

OBJECTIVEStudents will be able to solve inequali-ties involving polynomials and rationalfunctions by using both algebraic andgraphical techniques.

MOTIVATEAsk students to suggest ways to solve

�x �3

2� � �3x2�x

1� 0

algebraically or graphically.

TEACHING NOTEThis section extends the ideas of SectionP.6 to more complicated functions. Signcharts are introduced and the methodsof Sections 2.4 and 2.7 for finding zeros,asymptotes, and factorizations areapplied.

LESSON GUIDEDay 1: Polynomial InequalitiesDay 2: Rational and Other Inequalities;Applications

Figure 2.71 The graph off (x) � (x � 3) (x2 � 1)(x � 4)2. (Example 1)

[–4, 6] by [–100, 200]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 98

SECTION 2.9 Solving Inequalities in One Variable 99

• The solution of �x � 3��x2 � 1��x � 4�2 0 is �3, ∞�.

• The solution of �x � 3��x2 � 1��x � 4�2 0 is ��∞, �3�.

• The solution of �x � 3��x2 � 1��x � 4�2 � 0 is ��∞, �3�.

Example 1 illustrates some important general characteristics of polyno-mial functions and polynomial inequalities. The polynomial functionf �x� � �x � 3��x2 � 1��x � 4�2 in Example 1 and Figure 2.71

• changes sign at its real zero of odd multiplicity �x � �3�;

• touches the x-axis but does not change sign at its real zero of evenmultiplicity �x � 4�;

• has no x-intercepts or sign changes at its nonreal complex zeros associatedwith the irreducible quadratic factor �x2 � 1�.

This is consistent with what we learned about the relationships between zerosand graphs of polynomial functions in Sections 2.3 and 2.6. The real zeros andtheir multiplicity together with the end behavior of a polynomial function giveus sufficient information about the polynomial to sketch its graph well enoughto obtain a correct sign chart without considering the signs of the factors. SeeFigure 2.72.

Figure 2.72 The sign chart and graph of f (x) � (x � 3)(x2 � 1)(x � 4)2 overlaid.

x–3 4Negative due to

end behaviorPositive due tomultiplicity of

zeros

Positive due toend behavior

Odd multiplicity:Sign change

Even multiplicity:No sign change

So far in this section all of the polynomials have been presented in factoredform and all of the inequalities have had zero on one of the sides. Examples2 and 3 show us how to solve polynomial inequalities when they are not givenin such a convenient form.

Sketching a Graph of a Polynomial from Its Sign ChartUse your knowledge of end behavior and multiplicity of real zeros tocreate a sign chart and sketch the graph of the function. Check yoursign chart using the factor method of Example 1. Then check yoursketch using a grapher.

1. f �x� � 2�x � 2�3�x � 3�2

2. f �x� � ��x � 2�4�x � 1��2x2 � x � 1�

3. f �x� � 3�x � 2�2�x � 4�3��x2 � 2�

EXPLORATION 1

EXPLORATION EXTENSIONSFor your graph of question 1, for whatvalues of x is f (x) 0? And for whatvalues of x is f (x) 0?

TEACHING NOTEThis section presents two types of signcharts: one type is based on the signsof the factors (as shown in Example 1),and the other type is based on endbehavior and multiplicity (as shown inFigure 2.72). Using these two methodsgives students a deep understanding ofseveral important concepts and a wayto check their results, as in Exploration 1.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 99


EXAMPLE 2 Solving a polynomial inequality analyticallySolve 2x3 � 7x2 � 10x � 24 0 analytically.

SOLUTION Let f �x� � 2x3 � 7x2 � 10x � 24. The Rational Zeros Theoremsuggests several possible rational zeros of f for factoring purposes:

�1, �2, �3, �4, �6, �8, �12, �24, ��12

�, ��32

�.

A table or graph of f can suggest which of these candidates to try. In thiscase,x � 4 is a rational zero of f, as the following synthetic divisionshows:

4 2 �7 �10 24

8 4 �24

2 1 �6 0

The synthetic division allows us to start the factoring process, which canthen be completed using basic factoring methods:

f �x� � 2x3 � 7x2 � 10x � 24

� �x � 4��2x2 � x � 6�

� �x � 4��2x � 3��x � 2�

So the zeros of f are 4, 3�2, and �2. They are all real and all of multiplicity1, so each will yield a sign change in f �x�. Because the degree of f is oddand its leading coefficient is positive, the end behavior of f is given by

limx→∞

f �x� � ∞ and limx→�∞

f �x� � �∞.

Our analysis yields the following sign chart:

Sign Sign Signchange change change

Negative due to Positive Negative Positive due tox

end behavior�2 3�2 4

end behavior

The solution of 2x3 � 7x2 � 10x � 24 0 is ��2, 3�2� � �4, ∞�.

EXAMPLE 3 Solving a polynomial inequality graphicallySolve x3 � 6x2 � 2 � 8x graphically.

SOLUTION First we rewrite the inequality as x3 � 6x2 � 8x � 2 � 0. Thenwe let f �x� � x3 � 6x2 � 8x � 2 and find the real zeros of f graphically asshown in Figure 2.73. The three real zeros are approximately 0.32, 1.46, and4.21. The solution consists of the x values for which the graph is on orbelow the x-axis. So the solution of x3 � 6x2 � 2 � 8x is approximately��∞, 0.32� � 1.46, 4.21�.

The end points of these intervals are only accurate to two decimal places.We use square brackets because the zeros of the polynomial are solutions ofthe inequality, even though we only have approximations of their values.



Figure 2.73 The graph off (x) � x3 � 6x2 � 8x � 2, with one ofthree real zeros highlighted. (Example 3)

[–2, 5] by [–8, 8]

ZeroX=.32486913 Y=0

Worth Trying

You may wish to make a table or graph forthe function f in Example 2 to support theanalytical approach used.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 100


When a polynomial function has no sign changes, the solutions of the associatedinequalities can look a bit unusual, as illustrated in Example 4.

EXAMPLE 4 Solving polynomial inequalities withunusual answers

(a) The inequalities associated with the strictly positive polynomial functionf �x� � �x2 � 7��2x2 � 1� have unusual solution sets. We use Figure 2.74aas a guide to solving the inequalities:

• The solution of �x2 � 7��2x2 � 1� 0 is ��∞, ∞�, all real numbers.

• The solution of �x2 � 7��2x2 � 1� 0 is also ��∞, ∞�.

• The solution set of �x2 � 7��2x2 � 1� 0 is empty. We sometimes sayan inequality of this sort has no solution.

• The solution set of �x2 � 7��2x2 � 1� � 0 is also empty.

(b) The inequalities associated with the nonnegative polynomial functiong�x� � �x2 � 3x � 3��2x � 5�2 also have unusual solution sets. We useFigure 2.74b as a guide to solving the inequalities:

• The solution of �x2 � 3x � 3��2x � 5�2 0 is ��∞, �5�2� ��5�2, ∞�, all real numbers except x � �5�2, the lone real zero of g.

• The solution of �x2 � 3x � 3��2x � 5�2 0 is ��∞, ∞�, all real numbers.

• The solution set of �x2 � 3x � 3��2x � 5�2 0 is empty.

• The solution of �x2 � 3x � 3��2x � 5�2 � 0 is the single numberx � �5�2.

Rational InequalitiesA polynomial function p �x� is positive, negative, or zero for all real numbers x,but a rational function r �x� can be positive, negative, zero, or undefined. In par-ticular, a rational function is undefined at the zeros of its denominator. So whensolving rational inequalities we modify the kind of sign chart used in Example 1to include the real zeros of both the numerator and the denominator as locationsof potential sign change.

EXAMPLE 5 Creating a sign chart for a rational functionLet r �x� � �2x � 1��x � 3��x � 1��. Determine the values of x that causer �x� to be (a) zero,(b) undefined. Then make a sign chart to determine thevalues of x that cause r �x� to be (c) positive,(d) negative.

SOLUTION(a) The real zeros of r �x� are the real zeros of the numerator 2x � 1. So r �x�is zero if x � �1�2.

(b) r �x� is undefined when the denominator �x � 3��x � 1� � 0. So r �x� isundefined if x � �3 or x � 1.


Figure 2.74 The graphs of (a) f (x) � (x2 � 7)(2x2 � 1) and (b) g(x) � (x2 � 3x � 3)(2x � 5)2. (Example 4)

[–4.7, 4.7] by [–20, 100]

(b)

[–4.7, 4.7] by [–20, 100]

(a)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 101


These findings lead to the following sign chart, with three points of potentialsign change:

Potential Potential Potentialsign change sign change sign change

�3 �1�2 1x

Analyzing the factors of the numerator and denominator yields:

��

��

��

� und. ��

��

��

� 0 ��

��

��

� und. ��

��

��

�

Negative Positive Negative Positivex

�3 �1�2 1

(c) So r �x� is positive if �3 x �1�2 or x 1, and the solution of�2x � 1��x � 3��x � 1�� 0 is ��3, �1�2� � �1, ∞�.

(d) Similarly, r �x� is negative if x �3 or �1�2 x 1, and the solutionof �2x � 1��x � 3��x � 1�� 0 is ��∞, �3� � ��1�2, 1�.

Figure 2.75 supports our findings because the graph of r is above the x-axisfor x in ��3, �1�2� � �1, ∞� and is below the x-axis for x in ��∞, �3� ��1�2, 1�.

EXAMPLE 6 Solving a rational inequality bycombining fractions

Solve 5��x � 3� � 3��x � 1� 0.

SOLUTION We combine the two fractions on the left-hand side of theinequality using the least common denominator �x � 3��x � 1�:

�x �

53

� � �x �

31

� 0 Original inequality

��x �

5�x3�

�

�x1�

�1�

��x �

3�x3�

�

�x3�

�1)

� 0 Use LCD to rewrite fractions.

0 Add fractions.

�5�xx�

�

53�

��x3�

x �

1�9

� 0 Distributive property

��x �

8x3�

�

�x4� 1�

� 0 Simplify.

��x �

2x3�

�

�x1� 1�

� 0 Divide both sides by 4.

This is the inequality of Example 5d. So the solution is ��∞, �3� ��1�2, 1�. Now try Exercise 49.

5�x � 1� � 3�x � 3��

�x � 3��x � 1�


Figure 2.75 The graph of r (x) � (2x � 1)�((x � 3)(x � 1)).(Example 5)

[–4.7, 4.7] by [–3.1, 3.1]

ALERTWhen solving a rational inequalitysome students will attempt to multiplyboth sides by the LCD without regardto the direction of the inequality sign.They need to realize that since the signof the LCD (and hence the direction ofthe inequality sign in the resultinginequality) may depend on x, thismethod will not work.

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 102


Other InequalitiesThe sign chart method can be adapted to solve other types of inequalities, andwe can support our solutions graphically as needed or desired.

EXAMPLE 7 Solving an inequality involving a radicalSolve �x � 3��x � 1� 0.

SOLUTION Let f �x� � �x � 3��x � 1�. Because of the factor �x � 1�, f �x�is undefined if x �1. The zeros off are 3 and �1. These findings, alongwith a sign analysis of the two factors, lead to the following sign chart:

0��

0��

Undefined�1

Negative3

Positivex

So the solution of �x � 3��x � 1� 0 is ��1 � 3, ∞�. The graph off inFigure 2.76 supports this solution.

EXAMPLE 8 Solving an inequality involving absolute valueSolve �

�

x

x

�

�

23�

� � 0.

SOLUTION Let f �x� � �x � 2��x � 3�. Because �x � 3� is in the denomi-nator, f �x� is undefined if x � �3. The only zero off is 2. These findings,along with a sign analysis of the two factors, lead to the following sign chart:

��

�

��

� und. ��

�

��

� 0 ��

��

�

Negative Negative Positivex

�3 2

So the solution of �x � 2��x � 3� � 0 is ��∞, �3� � ��3, 2�. The graphof f in Figure 2.77 supports this solution.

Applications

EXAMPLE 9 Designing a box—revisitedDixie Packaging Company has contracted with another firm to design boxeswith a volume of at least600 in.3. Squares are still to be cut from the cor-ners of a 20-in. by 25-in. piece of cardboard, with the flaps folded up tomake an open box. What size squares should be cut from the cardboard?(See Example 9 of Section 2.3 and Figure 2.32.)

SOLUTIONModelRecall that the volume V of the box is given by

V�x� � x�25 � 2x��20 � 2x�,


Now try Exercise 43.Figure 2.76 The graph off (x) � (x � 3)�x�� 1�. (Example 7)

[–4.7, 4.7] by [–3.1, 3.1]

Figure 2.77 The graph off (x) � (x � 3)�� x � 3 �. (Example 8)

[–7, 7] by [–8, 2]

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 103


where x represents both the side length of the removed squares and the heightof the box. To obtain a volume of at least 600 in.3, we solve the inequality

x�25 � 2x��20 � 2x� 600.

Solve GraphicallyBecause the width of the cardboard is 20 in., 0� x � 10, and we set ourwindow accordingly. In Figure 2.78, we find the values of x for which thecubic function is on or above the horizontal line. The solution is the interval1.66, 6.16�.

InterpretSquares with side lengths between 1.66 in. and 6.16 in., inclusive, should becut from the cardboard to produce a box with a volume of at least 600 in.3.

EXAMPLE 10 Designing a juice can—revisitedStewart Cannery will package tomato juice in 2-liter �2000 cm3� cylindricalcans. Find the radius and height of the cans if the cans have a surface areathat is less than 1000 cm2. (See Example 7 of Section 2.8 and Figure 2.70.)

SOLUTIONModelRecall that the surface area S is given by

S�r� � 2�r2 � �40

r

00�.

So the inequality to be solved is

2�r2 � �40

r

00� 1000.

Solve GraphicallyFigure 2.79 shows the graphs of y1 � S�r� � 2�r 2 � 4000�r and y2 � 1000. Using grapher methods we find that the two curves intersect atapproximately r � 4.619. . . and r � 9.654. . . . (We carry all the extradecimal places for greater accuracy in a computation below.) So the surfacearea is less than 1000 cm3 if

4.62 r 9.65.

The volume of a cylindrical can is V � �r 2h and V � 2000. Using substi-tution we see that h � 2000��r 2�. To find the values for h we build adouble inequality for 2000��r 2�.

4.62 r 9.65 Original inequality

4.622 r 2 9.652 0 a b ⇒ a2 b2.

� • 4.622 �r2 � • 9.652 Multiply by �.

�� • 4

1.622� �

�

1r2� �

� • 91.652� 0 a b ⇒ �

1a

� �b1�.


Figure 2.78 The graphs of y1 � x(25 � 2x)(20 � 2x) and y2 � 600.(Example 9)

[0, 10] by [0, 1000]

IntersectionX=1.658749 Y=600

Figure 2.79 The graphs of y1 � 2�x2 � 4000�x and y2 � 1000.(Example 10)

[0, 20] by [0, 3000]

FOLLOW-UPAsk students to discuss why one mustfind the zeros of both the numeratorand denominator to solve a rationalinequality of the form p(x)�h(x) 0.

ASSIGNMENT GUIDEDay 1: Ex. 3–18, multiples of 3Day 2: Ex. 18–48, multiples of 3, 55–58,61, 62, 64, 74NOTES ON EXERCISESEx. 56–62 include many opportunitiesfor developing students’ problem-solving skills.Ex. 65–70 provide practice withstandardized tests.

COOPERATIVE LEARNINGGroup Activity: Ex. 73ONGOING ASSESSMENTSelf-Assessment: Ex. 1, 11, 15, 21, 25, 43, 49,53, 59, 61Embedded Assessment: Ex. 54, 61

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 104


��

2•

040.6022� �

2�

00r 20

� ��

2•

090.6052� Multiply by 2000.

��4

2.601090. . .�2� h �

��9.2605040. . .�2� Use the extra decimal places now.

29.83 h 6.83 Compute.

InterpretThe surface area of the can will be less than 1000 cm3 if its radius isbetween 4.62 cm and 9.65 cm and its height is between 6.83 cm and29.83 cm. Now try Exercise 61.

In Exercises 1–4, use limits to state the end behaviorof the function.

1. f �x� � 2x3 � 3x2 � 2x � 1 limx→∞

f(x) � ∞; limx→�∞

f(x) � �∞2. f �x� � �3x4 � 3x3 � x2 � 1

3. g�x� � �x3 �

x2�

x2

2� 1

�

4. g�x� � �2x2 �

x �

3x1

� 1�

In Exercises 5–8, combine the fractions and reduce youranswer to lowest terms.

5. x2 � �5x

� (x3 � 5)�x 6. x2 � �3x

� (x3 � 3)�x

7. �2x

x� 1� � �

x �

23

� 8. �x �

x1

� � �3xx�

�

14

�

In Exercises 9 and 10,(a) list all the possible rational zeros ofthe polynomial and (b) factor the polynomial completely.

9. 2x3 � x2 � 4x � 3 10. 3x3 � x2 � 10x � 8

QUICK REVIEW 2.9 (For help, go to Sections A.2, A.3, and 2.3.)


In Exercises 1–6, determine the x values that cause the polyno-mial function to be (a) zero,(b) positive, and (c) negative.

1. f �x� � �x � 2��x � 1��x � 5�

2. f �x� � �x � 7��3x � 1��x � 4�

3. f �x� � �x � 7��x � 4��x � 6�2

4. f �x� � �5x � 3��x2 � 6��x � 1�

5. f �x� � �2x2 � 5��x � 8�2�x � 1�3

6. f �x� � �x � 2�3�4x2 � 1��x � 9�4

In Exercises 7–12, complete the factoring if needed, and solvethe polynomial inequality using a sign chart. Support graphically.

7. �x � 1��x � 3�2 0 (�1, 3) � (3, ∞)

8. �2x � 1��x � 2��3x � 4� � 0 (�∞, �1�2] � [4�3, 2]

9. �x � 1��x2 � 3x � 2� 0 (�∞, �1) � (1, 2)

10. �2x � 7��x2 � 4x � 4� 0 (7/2, ∞)

11. 2x3 � 3x2 � 11x � 6 0 [�2, 1�2] � [3, ∞)

12. x3 � 4x2 � x � 6 � 0 (�∞, �1] � [2, 3]

In Exercises 13–20, solve the polynomial inequality graphically.

13. x3 � x2 � 2x 0 [�1, 0] � [2, ∞)

14. 2x3 � 5x2 � 3x 0 (�∞, 0) � (1, 3�2)

15. 2x3 � 5x2 � x � 6 0 (�1, 3/2) � (2, ∞)

16. x3 � 4x2 � x � 4 � 0 (�∞, �1] � [1, 4]

17. 3x3 � 2x2 � x � 6 0 [�1.15, ∞)

18. �x3 � 3x2 � 9x � 4 0 (0.39, ∞)

19. 2x4 � 3x3 � 6x2 � 5x � 6 0 (3�2, 2)

20. 3x4 � 5x3 � 12x2 � 12x � 16 0 (�∞, �4�3] � [�1, ∞)

In Exercises 21–24, solve the following inequalities for the givenfunction f �x�.

(a) f �x� 0 (b) f �x� 0 (c) f �x� 0 (d) f �x� � 0

21. f �x� � �x2 � 4��2x2 � 3�22. f �x� � �x2 � 1��2 � 3x2�23. f �x� � �2x2 � 2x � 5��3x � 4�2

24. f �x� � �x2 � 4��3 � 2x�2

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 105


In Exercises 25–32, determine the x values that cause the functionto be (a) zero,(b) undefined,(c) positive, and (d) negative.

25. f �x� ��2x �

x3�

��x1

� 4�� 26. f �x� ��

�2x �

x7�

��x5

� 1��

27. f �x� � x�x�� 3� 28. f �x� � x2�2x � 9�

29. f �x� ��2x

��

x1�

��x

5�� 1�

� 30. f �x� ��x �

x

4��

�

1

x�� 2��

31. f �x� � ��2x �

�x5�

��4�

x2

�� 3�� 32. f �x� ��

�x �

3

3

x

��

�x

1

�� 5��

In Exercises 33–44, solve the inequality using a sign chart.Support graphically.

33. �xx2�

�

14

� 0 34. �xx2�

�

29

� 0

35. �xx

2

2�

�

11

� � 0 [�1, 1] 36. �xx

2

2�

�

44

� 0

37. �xx

2

2

�

�

4xx�

�

124

� 0 38. �xx

2

2�

�

36xx�

�

190

� 0 (�5, 2)

39. �xx

2

3

�

�

1x

� 0 40. �xx

3

2�

�

42x

� � 0

41. x�x � 2� 0 42. ��

xx

�

�

32�

� 0

43. �2x � 1��x�� 4� 0 44. �3x � 4��2�x�� 1� 0

In Exercises 45–54, solve the inequality.

45. �x�

3

x�x�

�

3�22�

� 0 (0, 2) 46. �x�x�x

�

�

53�4

�� 0

47. x2 � �2x

� 0 48. x2 � �4x

� 0

49. �x �

11

� � �x �

13

� � 0 50. �x �

12

� � �x �

21

� 0

51. �x � 3��x � 1� 0 52. �3x � 5�2�x � 2� 0

53. ��x

��

2

5

x

��

x �

3�2�

� 0 54. �x

�

2�xx

�

�

4

1��3

� 0

55. Writing to Learn Write a paragraph that explains two waysto solve the inequality 3�x � 1� � 2 � 5x � 6.

56. Company Wages Pederson Electric Co. charges $25 perservice call plus $18 per hour for home repair work. Howlong did an electrician work if the charge was less than$100? Assume the electrician rounds off the time to thenearest quarter hour.

57. Connecting Algebra and Geometry Consider the collec-tion of all rectangles that have lengths 2 in. less than twicetheir widths. Find the possible widths (in inches) of theserectangles if their perimeters are less than 200 in.

58. Planning for Profit The Grovenor Candy Co. finds that thecost of making a certain candy bar is $0.13 per bar. Fixedcosts amount to $2000 per week. If each bar sells for $0.35,find the minimum number of candy bars that will earn thecompany a profit.9091 candy bars

59. Designing a Cardboard Box Picaro’sPackaging Plant wishes to design boxeswith a volume of not more than100 in.3 Squares are to be cut from thecorners of a 12-in. by 15-in. piece ofcardboard (see figure), with the flapsfolded up to make an open box. Whatsize squares should be cut from thecardboard?

60. Cone Problem Beginning with a circular piece of paperwith a 4-inch radius, as shown in (a), cut out a sector withan arc of length x. Join the two radial edges of the remain-ing portion of the paper to form a cone with radius r andheight h, as shown in (b). What length of arc will producea cone with a volume greater than 21 in.3?

61. Design a Juice Can Flannery Cannery packs peaches in0.5-L cylindrical cans.

(a) Express the surface area Sof the can as a function of theradius x (in cm). S � 2�x 2 � 1000�x

(b) Find the dimensions of the can if the surface is less than900 cm2.

(c) Find the least possible surface area of the can.

Design Engineering

0

1000

2000

3000

5 10Radius

Sur

face

are

a

15x

S

(a)

4 in.4 in.

sector

x

h

r

(b)

12 in.

15 in.

xx

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 106


62. Resistors The total electrical resistance R of two resistorsconnected in parallel with resistances R1 and R2 is givenby

�R1

� � �R1

1� � �

R1

2�.

One resistor has a resistance of 2.3 ohms. Let x be the resis-tance of the second resistor.

(a) Express the total resistance R as a function of x.

(b) Find the resistance in the second resistor if the totalresistance of the pair is at least 1.7 ohms.

63. Per Capita Income The U.S. average per capita incomefor several years from 1990 to 2000 is given in Table2.24. Let x � 0 represent 1990,x � 1 represent 1991,and so forth.

(a) Find the quadratic regression model for the data andsuperimpose its graph on a scatter plot of the data.

(b) Use the model to predict when the per capita incomeexceeds $40,000.

64. Annual Housing Cost Theaverage annual expenditure for housing for several yearsfrom 1990 to 1999 is given in Table 2.25. Let x � 0 represent 1990,x � 1 represent 1991, and so forth.

(a) Find the quadratic regression model for the data andsuperimpose its graph on a scatter plot of the data.

(b) Use the model to predict when the average annualexpenditure for housing exceeds $15,000.

Standardized Test Questions65. True or False The graph of f �x� � x4�x � 3�2�x � 1�3

changes sign at x � 0. Justify your answer.

66. True or False The graph r �x� � ��x �22x��x

1� 1�� changes

sign at x � �2. Justify your answer.


67. Which of the following is the solution to x2 x?

(a) �0, ∞� (b) �1, ∞� (c) �0, 1�(d) ��∞, 1� (e) ��∞, 0� � �1, ∞� (c)

68. Which of the following is the solution to ��x �1

2�2� 0?

(a) ��2, ∞� (b) All x � �2

(c) All x � 2 (d) All real numbers

(e) There are no solutions.(a)

69. Which of the following is the solution to �x �

x2

3� 0?

(a) ��∞, 3� (b) ��∞, 3�(c) ��∞, 0� � �0, 3� (d) ��∞, 0� � �0, 3�(e) There are no solutions.(d)

70. Which of the following is the solution to (x2 � 1)2 � 0?

(a) { �1, 1} (b) {1} (c) �1, 1�(d) 0, 1� (e) There are no solutions.(a)

ExplorationsIn Exercises 71 and 72, find the vertical asymptotes and interceptsof the rational function. Then use a sign chart and a table of valuesto graph the function by hand. Support your result using a grapher.(Hint: You may need to graph the function in more than one win-dow to see different parts of the overall graph.)

71. f �x� � ��xx

�

�

13��xx

�

�

21��

2

� 72. g�x� � ��xx2�

�

34�x

4

�

Table 2.25 Average Annual Housing Cost

Year Amount (dollars)

1990 8,7031993 9,6361994 10,1061995 10,4651996 10,7471997 11,2721998 11,7131999 12,057

Source: U.S. Bureau of the Census, Consumer Expenditures,Statistical Abstract of the United States, 2001

Table 2.24 Per Capita Income


1990 19,6141991 20,1261992 21,1051993 21,7351994 22,5931995 23,5711996 24,6601997 25,8761998 27,3171999 28,5342000 30,069

Source: U.S. Bureau of the Census, Survey of CurrentBusiness, Statistical Abstract of the United States, 2001

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 107


Extending the Ideas73. Group Activity Looking Ahead to Calculus Let

f �x� � 3x � 5.

(a) Assume x is in the interval defined by �x � 3� 1�3.Give a convincing argument that � f �x� � 4� 1.

(b) Writing to Learn Explain how (a) is modeled by thefigure at the top of the next column.

(c) Show how the algebra used in (a) can be modified toshow that if �x � 3� 0.01, then � f �x� � 4� 0.03. Howwould the figure below change to reflect these inequalities?

74. Writing to Learn Boolean Operators The Test menu ofmany graphers contains inequality symbols that can be usedto construct inequality statements, as shown in (a). Ananswer of 1 indicates the statement is true, and 0 indicatesthe statement is false. In (b), the graph of Y1 � x2 � 4 0 is shown using Dot mode and the window�4.7, 4.7� by �3.1, 3.1�. Experiment with the Test menu,and then write a paragraph explaining how to interpret thegraph in (b).

In Exercises 75–76, use the properties of inequality from Chapter P to prove the statement.

75. If 0 a b, then a2 b2.

76. If 0 a b, then �1a

� �1b

�.

[–4.7, 4.7] by [–3.1, 3.1]

(b)

3≥2

7≥7

4≥9

N

1

1

0

(a)

7

321

–1–2

y

456

x–2–3 –1 2 5431

f(x) = 3x – 5

I’m working on a Ph.D. in computational neuroscience.I became interested in this field after working as a soft-

ware engineer. Now, I’m here, a back-to-school mom atan engineering school in Switzerland! After years of soft-ware programming, I found I had forgotten most of mymathematics, but I’ve found it’s like any other skill—itjust takes practice.

In this field we use computer simulations to explore waysof understanding what neurons do in the brain and the restof our nervous systems. The brain contains so many neu-rons—and so many different kinds of them—that if we tryto make a really “realistic” model of a part of the brain,not only do the simulations run very slowly on the com-puter, but also they can be too complicated to understand!

What we do is use very simple models for the individualneurons. We use mathematics to analytically calculatequantities such as the response of a group of neurons to a

specific input signal or how much information the neu-rons can transmit under various conditions. Then we usecomputer simulations to test whether our theoretical pre-diction really works. When the theory matches the exper-iment, it’s really exciting!

An equation that is commonlyused in my field is that for themembrane potential of a neu-ron. This is the amount of cur-rent the neuron is able to storebefore it “fires” an action poten-tial, which is how it communi-cates to other neurons, or evenmuscles, telling them to move.If we keep some of the quanti-ties in the equation constant, wecan solve for the others. Forinstance, if the input current and

resistance are kept constant, we can solve for the mem-brane potential.

Math at Work

AliAlix Kax KammakakaaokokalanalaniiHeHerrmrrmanannn

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 108

SECTION 2.9 Key Ideas 109

CHAPTER 2 Key IdeasPROPERTIES, THEOREMS, AND FORMULAS

PROCEDURES

GALLERY OF FUNCTIONS

f (x) � x f (x) � x2 f (x) � x3 f (x) � 1/x � x � 1

f (x) � �x� � x1/2 f (x) � �3 x� � x1/3 f (x) � 1/x2 � x�2

[–4.7, 4.7] by [–3.1, 3.1]

Inverse-Square

[–4.7, 4.7] by [–3.1, 3.1]

Cube Root

[–4.7, 4.7] by [–3.1, 3.1]

Square Root

[–4.7, 4.7] by [–3.1, 3.1]

Reciprocal

[–4.7, 4.7] by [–3.1, 3.1]

Cubing

[–4.7, 4.7] by [–1, 5]

Squaring

[–4.7, 4.7] by [–3.1, 3.1]

Identity

Regression Analysis (p. 162)Completing the Square (p. XXX)Polynomial Long Division (p. 199)

Synthetic Division (p. 202)Solving Inequalities Using Sign Charts (p. 243)

Properties of the Correlation Coefficient, r (p. 160)Vertex Form of a Quadratic Function (p. 164)Vertical Free-Fall Motion (p. 166)Theorem Local Extrema and Zeros of Polynomial

Functions (p. 189)Leading Term Test for Polynomial End Behavior (p. 190)Zeros of Odd and Even Multiplicity (p. 192)Intermediate Value Theorem (p. 193)Division Algorithm for Polynomials (p. 200)Remainder Theorem (p. 201)Factor Theorem (p. 202)

Fundamental Connections for PolynomialFunctions (p. 202)

Rational Zeros Theorem (p. 205)Fundamental Theorem of Algebra (p. 220)Linear Factorization Theorem (p. 220)Fundamental Polynomial Connections in the

Complex Case (p. 221)Complex Conjugate Zeros (p. 222)Factors of a Polynomial with Real Coefficients (p. 224)Polynomial Function of Odd Degree (p. 224)

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 109


The collection of exercises marked in red could be used as achapter test.

In Exercises 1 and 2, write an equation for the linear functionfsatisfying the given conditions. Graph y � f �x�.

1. f ��3� � �2 and f �4� � �9

2. f ��3� � 6 and f �1� � �2

In Exercises 3 and 4, describe how to transform the graph off �x� � x2 into the graph of the given function. Sketch the graphby hand and support your answer with a grapher.

3. h�x� � 3�x � 2�2 � 4

4. g�x� � ��x � 3�2 � 1

In Exercises 5–8, find the vertex and axis of the graph of thefunction. Support your answer graphically.

5. f �x� � �2�x � 3�2 � 5 6. g�x� � 4�x � 5�2 � 7

7. f �x� � �2x2 � 16x � 31 8. g�x� � 3x2 � 6x � 2

In Exercises 9 and 10, write an equation for the quadraticfunction whose graph contains the given vertex and point.

9. Vertex ��2, �3�, point �1, 2� y � 5/9(x � 2)2 � 3

10. Vertex ��1, 1�, point �3, �2� y � �3/16(x � 1)2 � 1

In Exercises 11 and 12, write an equation for the quadraticfunction with graph shown, given one of the labeled points isthe vertex of the parabola.

11. 12.

In Exercises 13–16, graph the function in a viewing windowthat shows all of its extrema and x-intercepts.

13. f �x� � x2 � 3x � 40 14. f �x� � �8x2 � 16x � 19

15. f �x� � x3 � x2 � x � 5 16. f �x� � x3 � x2 � 20x � 2

In Exercises 17 and 18, write the statement as a power functionequation. Let k be the constant of variation.

17. The surface area Sof a sphere varies directly as the squareof the radius r. S � kr 2

18. The force of gravity F acting on an object is inverselyproportional to the square of the distance d from the objectto the center of the earth.F � k /d 2

In Exercises 19 and 20, write a sentence that expresses therelationship in the formula, using the language of variation orproportion.

19. F � kx, where F is the force it takes to stretch a spring xunits from its unstressed length and k is the spring’s forceconstant.

20. A � � • r 2, where A and r are the area and radius of a circleand � is the usual mathematical constant.

In Exercises 21–24, state the values of the constants k and a forthe function f �x� � k • xa. Describe the portion of the curve thatlies in Quadrant I or IV. Determine whether f is even, odd, orundefined for x 0. Describe the rest of the curve if any. Graphthe function to see whether it matches the description.

21. f �x� � 4x1�322. f �x� � �2x3�4

23. f �x� � �2x�324. f �x� � �2�3�x�4

In Exercises 25–28, divide f �x� by d�x�, and write a summarystatement in polynomial form.

25. f �x� � 2x3 � 7x2 � 4x � 5; d�x� � x � 3

26. f �x� � x4 � 3x3 � x2 � 3x � 3; d�x� � x � 2

27. f �x� � 2x4 � 3x3 � 9x2 � 14x � 7; d�x� � x2 � 4

28. f �x� � 3x4 � 5x3 � 2x2 � 3x � 6; d�x� � 3x � 1

In Exercises 29 and 30, use the Remainder Theorem to find theremainder when f �x� is divided by x � k. Check by usingsynthetic division.

29. f �x� � 3x3 � 2x2 � x � 5; k � �2

30. f �x� � �x2 � 4x � 5; k � 3

In Exercises 31 and 32, use the Factor Theorem to determinewhether the first polynomial is a factor of the second polynomial.

31. x � 2; x3 � 4x2 � 8x � 8

32. x � 3; x3 � 2x2 � 4x � 2

In Exercises 33 and 34, use synthetic division to prove that thenumber k is an upper bound for the real zeros of the function f.

33. k � 5; f �x� � x3 � 5x2 � 3x � 4

34. k � 4; f �x� � 4x4 � 16x3 � 8x2 � 16x � 12

In Exercises 35 and 36, use synthetic division to prove that thenumber k is a lower bound for the real zeros of the function f.

35. k � �3; f �x� � 4x4 � 4x3 � 15x2 � 17x � 2

36. k � �3; f �x� � 2x3 � 6x2 � x � 6

In Exercises 37 and 38, use the Rational Zeros Theorem to writea list of all potential rational zeros. Then determine which ones,if any, are zeros.

37. f �x� � 2x4 � x3 � 4x2 � x � 6

38. f �x� � 6x3 � 20x2 � 11x � 7

[–10, 5] by [–8, 8]

(–4, 5)

(0, –3)

[–4, 8] by [–4, 10]

(3, –2)

(5, 0)

CHAPTER 2 Review Exercises

DWFK-PC5-02_v2 01/23/03 9:05 AM Page 110

SECTION 2.9 Review Excercises 111

In Exercises 39–46, perform the indicated operation, and writethe result in the standard form a � bi.

39. �3 � 2i � � ��2 � 5i � 40. �5 � 7i � � �3 � 2i �41. �1 � 2i ��3 � 2i � 7 � 4i 42. �1 � i �3 �2 � 2i

43. �1 � 2i �2�1 � 2i �2 25 44. i 29 i

45. ��1�6� 4i 46. �21

�

�

35ii

� �1/2 � 1/2i

In Exercises 47 and 48, solve the equation.

47. x2 � 6x � 13 � 0 3 � 2i 48. x2 � 2x � 4 � 0

In Exercises 49–52, match the polynomial function with itsgraph. Explain your choice.

49. f �x� � �x � 2�2 (c) 50. f �x� � �x � 2�3 (d)

51. f �x� � �x � 2�4 (b) 52. f �x� � �x � 2�5 (a)

In Exercises 53–56, find all of the real zeros of the function, find-ing exact values whenever possible. Identify each zero as rationalor irrational. State the number of nonreal complex zeros.

53. f �x� � x4 � 10x3 � 23x2

54. k�t� � t4 � 7t2 � 12

55. h�x� � x3 � 2x2 � 8x � 5

56. k�x� � x4 � x3 � 14x2 � 24x � 5

In Exercises 57–60, find all of the zeros and write a linearfactorization of the function.

57. f �x� � 2x3 � 9x2 � 2x � 30

58. f �x� � 5x3 � 24x2 � x � 12

59. f �x� � 6x4 � 11x3 � 16x2 � 11x � 10

60. f �x� � x4 � 8x3 � 27x2 � 50x � 50, given that 1� 2i isa zero.

In Exercises 61–64, write the function as a product of linear andirreducible quadratic factors all with real coefficients.

61. f �x� � x3 � x2 � x � 2

62. f �x� � 9x3 � 3x2 � 13x � 1

63. f �x� � 2x4 � 9x3 � 23x2 � 31x � 15

64. f �x� � 3x4 � 7x3 � 3x2 � 17x � 10

In Exercises 65–70, write a polynomial function with realcoefficients whose zeros and their multiplicities include thoselisted.

65. Degree 3; zeros:�5�, ��5�, 3 x 3 � 3x 2 � 5x � 15

66. Degree 2;�3 only real zerox 2 � 6x � 9

67. Degree 4; zeros: 3,�2, 1�3, �1�2

68. Degree 3; zeros: 1� i, 2 x 3 � 4x 2 � 6x � 4

69. Degree 4; zeros:�2(multiplicity 2), 4(multiplicity 2)

70. Degree 3; zeros: 2� i, �1, and f �2� � 6

In Exercises 71 and 72, describe how the graph of the givenfunction can be obtained by transforming the graph of thereciprocal function f �x� � 1�x. Identify the horizontal andvertical asymptotes.

71. f �x� � ��

xx�

�

57

� 72. f �x� � �3xx�

�

25

�

In Exercises 73–76, find the asymptotes and intercepts of thefunction, and graph it.

73. f �x� � 74. f �x� �

75. f �x� � 76. g�x� �

In Exercises 77–78, find the intercepts and analyze and draw thegraph of the given rational function.

77. f �x� ��x3 � x

x

2

�

�

22x � 5� 78. f �x� � �

�x4

x�

�

x2

1� 1

�

In Exercises 79–86, solve the equation or inequality algebraically,and support graphically.

79. 2x � �1x2� � 11 x � �

32� or x � 4

80. �x �

x2

� � �x �

53

� � �x2 �

2x5

� 6� x � �5

81. 2x3 � 3x2 � 17x � 30 0 (�∞, �5/2) � (�2, 3)

82. 3x4 � x3 � 36x2 � 36x � 16 0 (�∞, �4� � [�1/3, ∞)

83. 0 84. �x2

x�

2 �

x �

76

� 1

85. �2x � 1�2�x � 3� � 0 86. 0

87. Plot �3 �2i in the complex plane.

88. Writing to Learn Determine whether

f �x� � x5 � 10x4 � 3x3 � 28x2 � 20x � 2

has a zero outside the viewing window. Explain.

(x � 1)�x � 4��

�x � 3�

x � 3�x2 � 4

x2 � 3x � 7��

x � 3x2 � 4x � 5��

x � 3

2x2 � 7��x2 � x � 6

x2 � x � 1��

x2 � 1

(d)(c)

(b)(a)

DWFK-PC5-02_v2 01/23/03 9:06 AM Page 111


89. Launching a Rock Larry uses a slingshot to launch a rockstraight up from a point 6 ft above level ground with aninitial velocity of 170 ft�sec.

(a) Find an equation that models the height of the rock tseconds after it is launched and graph the equation.(See Example 7 in Section 2.1.)

(b) What is the maximum height of the rock? When will itreach that height?

(c) When will the rock hit the ground?

90. Volume of a Box Edgardo Paper Co. has contracted tomanufacture a box with no top that is to be made byremoving squares of width x from the corners of a 30-in.by 70-in. piece of cardboard.

(a) Find an equation that models the volume of the box.

(b) Determine x so that the box has a volume of5800 in.3.

91. Architectural Engineering Donoma, an engineer atJ. P. Cook, Inc., completes structural specifications for a255-ft-long steel beam anchored between two pilings 50 ftabove ground, as shown in the figure. She knows that whena 250-lb object is placed d feet from the west piling, thebeam bends s feet where

s � �8.5� 10�7�d2�255� d�.(a) Graph the function s.

(b) What are the dimensions of a viewing window thatshows a graph for the values that make sense in thisproblem situation?

(c) What is the greatest amount of vertical deflection s, andwhere does it occur?

(d) Writing to Learn Give a possible scenarioexplaining why the solution to (c) does not occur atthe halfway point.

92. Storage Container A liquid storage container on a truck isin the shape of a cylinder with hemispheres on each end asshown in the figure. The cylinder and hemispheres have thesame radius. The total length of the container is 140 ft.

(a) Determine the volume V of the container as a function ofthe radius x.

(b) Graph the function y � V�x).

(c) What is the radius of the container with the largestpossible volume? What is the volume?

93. Pell Grants The maximum loan permitted under the federalstudent-aid program is given in Table 2.26 for several years.Let x � 0 represent 1990,x � 1 represent 1991, and soforth.

(a) Find a quadratic regression model for the Pell Grantamounts, and graph it together with a scatter plot of thedata.

(b) Find a quartic regression model for the Pell Grantamounts, and graph it together with a scatter plot of thedata.

(c) Use each regression equation to predict the amount of aPell Grant in 2006.

(d) Writing to Learn Determine the end behavior of thetwo regression models. What does the end behavior sayabout future Pell Grant amounts?

Table 2.26 Maximum Pell Grant


1990 23001991 24001992 24001993 23001994 23001995 23401996 24701997 27001998 30001999 31252000 33002001 37502002 4000

Source: U.S. Education Department, as reported in TheChronicle of Higher Education, February 15, 2002

140

x

x

x

ds

West East

[–5, 5] by [–50, 50]

DWFK-PC5-02_v2 01/23/03 9:06 AM Page 112

SECTION 2.9 Review Excercises 113

94. National Institute of Health Spending Table 2.27 showsthe spending at the National Institute of Health for severalyears. Let x � 0 represent 1990,x � 1 represent 1991, andso forth.

(a) Find a linear regression model, and graph it togetherwith a scatter plot of the data.

(b) Find a quadratic regression model, and graph it togetherwith a scatter plot of the data.

(c) Use the linear and quadratic regression models to esti-mate when the amount of spending will exceed $30 billion.

95. Breaking Even Midtown Sporting Goods has determinedthat it needs to sell its soccer shinguards for $5.25 a pair inorder to be competitive. It costs $4.32 to produce each pairof shinguards, and the weekly overhead cost is $4000.

(a) Express the average cost that includes the overhead ofproducing one shinguard as a function of the number x ofshinguards produced each week.

(b) Solve algebraically to find the number of shinguards thatmust be sold each week to make $8000 in profit. Supportyour work graphically.

96. Deer Population The number of deer P at any timet (in years) in a federal game reserve is given by

P�t� � .

(a) Find the number of deer when t is 15, 70, and 100.

(b) Find the horizontal asymptote of the graph of y � P�t�.(c) According to the model, what is the largest possible deerpopulation?

97. Resistors The total electrical resistance R of tworesistors connected in parallel with resistances R1 and R2

is given by

�R1

� � �R1

1� � �

R1

2�.

The total resistance is 1.2 ohms. Let x � R1.

(a) Express the second resistance R2 as a function of x.

(b) Find R2 if x1 is 3 ohms.

98. Acid Mixture Suppose that x ounces of distilled water areadded to 50 oz of pure acid.

(a) Express the concentration C�x� of the new mixture as afunction of x.

(b) Use a graph to determine how much distilled watershould be added to the pure acid to produce a new solutionthat is less than 60% acid.

(c) Solve (b) algebraically.

99. Industrial Design Johnson Cannery will pack peaches in1-L cylindrical cans. Let x be the radius of the base of thecan in centimeters.

(a) Express the surface area Sof the can as a function of x.

(b) Find the radius and height of the can if the surface areais 900 cm2.

(c) What dimensions are possible for the can if the surfacearea is to be less than 900 cm2?

100. Industrial Design Gilman Construction is hired tobuild a rectangular tank with a square base and no top.The tank is to hold 1000 ft3 of water. Let x be a lengthof the base.

(a) Express the outside surface area Sof the tank as a func-tion of x.

(b) Find the length, width, and height of the tank if theoutside surface area is 600 ft2.

(c) What dimensions are possible for the tank if the outsidesurface area is to be less than 600 ft2?800� 640t

��20 � 0.8t

Table 2.27 Spending at the National

Institute of Health

Year Amount(billion)

1993 10.31994 11.01995 11.31996 11.91997 12.71998 13.61999 15.62000 17.92001 20.52002 23.6

Source: National Institute of Health as reported in TheChronicle of Higher Education November 26, 1999 andFebruary 15, 2002.

DWFK-PC5-02_v2 01/23/03 9:06 AM Page 113


CHAPTER 2 ProjectModeling the Height of a Bouncing BallWhen a ball is bouncing up and down on a flat surface, itsheight with respect to time can be modeled using a qua-dratic function. One form of a quadratic function is thevertex form:

y � a�x � h�2 � k

In this equation,y represents the height of the ball and xrepresents the elapsed time. For this project, you will usea motion detection device to collect distance and timedata for a bouncing ball, then find a mathematical modelthat describes the position of the ball.

EXPLORATIONS

1. If you collected motion data using a CBL2 or CBR™,a plot of height versus time or distance versus timeshould be shown on your grapher or computer screen.Either plot will work for this project. If you do nothave access to a CBL2�CBR™, enter the data fromthe table above into your grapher�computer. Create ascatter plot for the data.

2. Find values for a, h, and k so that the equation y �a�x � h�2 � k fits one of the bounces contained in thedata plot. Approximate the vertex �h, k� from your dataplot and solve for the value of a algebraically.

3. Change the values of a, h, and k in the model foundabove and observe how the graph of the function isaffected on your grapher or computer. Generalize howeach of these changes affects the graph.

4. Expand the equation you found in #2 above so that itis in the standard quadratic form:y � ax2 � bx � c.

5. Use your grapher or computer to select the datafrom the bounce you modeled above and then usequadratic regression to find a model for this dataset. (See your grapher’s guidebook for instructionson how to do this.) How does this model comparewith the standard quadratic form found in #4?

6. Complete the square to transform the regressionmodel to the vertex form of a quadratic and compareit to the original vertex model found in #2. (Roundthe values of a, b, and c to the nearest 0.001 beforecompleting the square if desired.)

Total Height Total Heightelapsed time of the ball elapsed time of the ball

(seconds) (meters) (seconds) (meters)

0.688 0 1.118 0.8280.731 0.155 1.161 0.8110.774 0.309 1.204 0.7760.817 0.441 1.247 0.7210.860 0.553 1.290 0.6500.903 0.643 1.333 0.5630.946 0.716 1.376 0.4520.989 0.773 1.419 0.3221.032 0.809 1.462 0.1691.075 0.828

DWFK-PC5-02_v2 01/23/03 9:06 AM Page 114

Documents

Polynomial,Power, andRational Functions CHAPTER 2 2 text... · Polynomial,Power, andRational Functions 2.1 Linear and Quadratic ... For students:Aha! Insight,Martin Gardner.W.H.Freeman,1978.Available