Upload
sandra-miller
View
410
Download
2
Embed Size (px)
Citation preview
Obj. 7 Polynomial Graphs
Unit 2 Quadratic and Polynomial Functions
Concepts and Objectives
� Objective #7
� Identify and interpret vertical and horizontal
translations
� Identify the end behavior of a function
� Identify the number of turning points of a function
� Use the Intermediate Value Theorem and the
Boundedness Theorem to locate zeros of a function
� Use the calculator to approximate real zeros
Graphing Polynomial Functions
� If we look at graphs of functions of the form ,
we can see a definite pattern:( ) =
nf x ax
( ) =2f x x ( ) =
3g x x
( ) =4h x x ( ) =
5j x x
Graphing Polynomial Functions
� For a polynomial function of degree n
� If n is even, the function is an even function.
� An even function has a range of the form (–∞, k] or
[k, ∞) for some real number k.
� The graph may or may not have a real zero
(x-intercept.)
� If n is odd, the function is an odd function.
� The range of an odd function is the set of all real
numbers, (–∞, ∞).
� The graph will have at least one real zero
(x-intercept).
Graphing Polynomial Functions
� Compare the graphs of the two functions:
( ) =2f x x
( ) = −2 2g x x
( ) =2h x x
( ) ( )= −2
1j x x
Graphing Polynomial Functions
� Vertical translation
� The graph of is shifted k units up if
k > 0 and |k| units down if k < 0.
� Horizontal translation
� The graph of is shifted h units to the
right if h > 0 and |h| units to the left if h < 0.
( ) = +nf x ax k
( ) ( )= −n
f x a x h
Graphing Polynomial Functions
� Example: Write the equation of the function of degree 3
graphed below.
This is an odd function.
The vertex is at (2, 3).
The vertex has been shifted up 3
units and to the right 2 units.
So, it’s going to be something like:
( ) ( )= − +3
32f x a x
•
Graphing Polynomial Functions
� Example (cont.):
To determine what a is, we can pick
a point and plug in values:
( ) =3 4f
( ) ( )= − + =3
3 3 2 3 4f a
+ =3 4a
= 1a
( ) ( )3
2 3f x x= − +
•
( ) ( )= − +3
2 3f x a x
Multiplicity and Graphs
� What is the multiplicity of ?
The zero 4 has multiplicity 5
� The multiplicity of a zero and whether the function is
even or odd determines what the graph does at a zero.
� A zero of multiplicity one crosses the x-axis.
� A zero of even multiplicity turns or “bounces” at the
x-axis .
� A zero of odd multiplicity greater than one crosses
the x-axis and “wiggles”.
( ) ( )= −5
4g x x
Turning Points and End Behavior
� The point where a graph changes direction (“bounces”
or “wiggles”) is called a turning point of the function.
� A function of degree n will have at most n – 1 turning
points, with at least one turning point between each
pair of adjacent zeros.
� The end behavior of a polynomial graph is determined by
the term with the largest exponent (the dominating
term).
� For example, has the same end
behavior as .( ) = − +
32 8 9f x x x
( ) =32f x x
End Behavior
� Example: Use symbols for end behavior to describe the
end behavior of the graph of each function.
1.
2.
3.
( ) = − + + −4 22 8f x x x x even function
opens downward
( ) = + − +3 22 3 5g x x x x odd function
increases
( ) = − + +5 32 1h x x x odd function
decreases
Intermediate Value Theorem
� This means that if we plug in two numbers and the
answers have different signs (one positive and one
negative), the function has to have crossed the x-axis
between the two values.
If f(x) defines a polynomial function with only real
coefficients, and if for real numbers a and b, the
values f(a) and f(b) are opposite in sign, then there
exists at least one real zero between a and b.
Intermediate Value Theorem
� Example: Show that has a real
zero between 2 and 3.
You can either plug the values in, or you can use
synthetic division to evaluate each value.
Since the sign changes, there must be a real zero
between 2 and 3.
( ) = − − +3 22 1f x x x x
− −2 1 2 1 1
1
2
0
0
–1
–2
–1
− −3 1 2 1 1
1
3
1
3
2
6
7
Intermediate Value Theorem
� If f(a) and f(b) are not opposite in sign, it does not
necessarily mean that there is no zero between a and b.
Consider the function, , at –1 and 3:( ) = − −2 2 1f x x x
f(–1) = 2 > 0 and f(3)= 2 >0
This would imply that there is no
zero between –1 and 3, but we can
see that f has two zeros between
those points.
Boundedness Theorem
Let f(x) be a polynomial function of degree n ≥ 1 with
real coefficients and with a positive leading coefficient.
If f(x) is divided synthetically by x – c, and
(a) if c > 0 and all numbers in the bottom row are
nonnegative, then f(x) has no zeros greater than c;
(b) if c < 0 and the numbers in the bottom row
alternate in sign, then f(x) has no zero less than c.
Boundedness Theorem
� Example: Show that the real zeros of
satisfy the following conditions,
a) No real zero is greater than 1
Since the bottom row numbers are all ≥ 0, f(x) has
no zero greater than 1.
( ) = + + −4 25 3 7f x x x x
−1 1 0 5 3 79
9
6
6
1
1
1
1 2
Boundedness Theorem
� Example: Show that the real zeros of
satisfy the following conditions,
b) No real zero is less than –2
Since the signs of the bottom numbers alternate, f(x)
has no zero less than –2.
( ) = + + −4 25 3 7f x x x x
− −2 1 0 5 3 730
–15
–18
9
4
–2
–2
1 23
Approximating Real Zeros
� Example: Approximate the real zeros of
Step 1: Enter the function into o
( ) = − − + +3 28 4 10f x x x x
Approximating Real Zeros
� Example: Approximate the real zeros of
Step 2: Press yr and then Á
( ) = − − + +3 28 4 10f x x x x
Approximating Real Zeros
� Example: Approximate the real zeros of
Step 3: Position the cursor at the far
left above the x-axis and press Í
Step 4: Move the cursor below the
x-axis and press Í
( ) = − − + +3 28 4 10f x x x x
Approximating Real Zeros
� Example: Approximate the real zeros of
Step 5: Our first zero is at –8.33594
( ) = − − + +3 28 4 10f x x x x
Approximating Real Zeros
� Example: Approximate the real zeros of
Repeat steps 1-5 to find the next two
zeros
#2: –0.9401088
( ) = − − + +3 28 4 10f x x x x
Approximating Real Zeros
� Example: Approximate the real zeros of
Repeat steps 1-5 to find the next two
zeros
#2: –0.9401088
#3: 1.2760488
( ) = − − + +3 28 4 10f x x x x
Homework
� College Algebra
� Page 352: 21-27 (×3), 48-69 (×3), 81
� HW: 24, 48, 54, 60, 63, 66