5.1 – Introduction to Quadratic Functions

Objectives: Define, identify, and graph quadratic functions.Multiply linear binomials to produce a quadratic expression.Standard: 2.8.11.E. Use equations to represent curves.

cbxaxxf 2)(

The Standard Form of a Quadratic Function is:

(A quadratic function is any function that can be written in the form f(x)= ax2 + bx + c, where a ≠ 0.)

I. Quadratic function is any function that can be written in the form f(x)= ax2 + bx + c, where a ≠ 0.

List a, b & c

FOIL First – Outer – Inner – Last

Ex 1. Let f(x) = (2x – 1)(3x + 5). Show that f represents a quadratic function. Identify a, b, and c when the function is written in the form f(x) = ax2 + bx + c.

Ex 2. Let f(x) = (2x – 5)(x - 2). Show that f represents a quadratic function. Identify a, b, and c when the function is written in the form f(x) = ax2 + bx + c.

List a, b & c

Show that each function is a quadratic function by writing it in the form f(x) = ax2 + bx + c. List a, b & c.

1. f(x) = (x – 3) (x + 8)

2. g(x) = (4 – x) (7 + x)

3. g(x) = -(x – 2) (x + 6)

4. f(x) = 3(x – 2) (x + 1)

5. g(x) = 2x(x + 5)

6. f(x) = (x – 4) (x + 4)

II. The graph of a quadratic function is called a parabola. Each parabola has an axis of symmetry, a line that divides the

parabola into two parts that are mirror images of each other. The vertex of a parabola is either the lowest point on the graph or

the highest point on the graph.

Example 1

Example 2

Ex 2. Identify whether f(x) = -2x2 - 4x + 1 has a maximum value or a minimum value at the vertex. Then give the approximate coordinates of the vertex.

First, graph the function:

Next, find the maximum value of the parabola (2nd, Trace):

Finally, max(-1, 3).

III. Minimum and Maximum Values

Let f(x) = ax2 + bx + c, where a ≠ 0. The graph of f is a parabola.If a > 0, the parabola opens up and the

vertex is the lowest point. The y-coordinate of the vertex is the minimum value of f.

If a < 0, the parabola opens down and the vertex is the highest point. The y-coordinate of the vertex is the maximum value of f.

Ex 1. State whether the parabola opens up or down and whether the y-coordinate of the vertex is the minimum value or the maximum value of the function. Then check by graphing it in your Y = button on your calculator. Remember: f(x) means the same thing as y!

a. f(x) = x2 + x – 6

b. g(x) = 5 + 4x – x2

c. f(x) = 2x2 - 5x + 2

d. g(x) = 7 - 6x - 2x2

Opens up, has minimum value

Opens down, has maximum value

Opens up, has minimum value

Opens down, has maximum value

Writing Activities

1. a. Give an example of a quadratic function that has a maximum value. How do you know that it has a maximum?

1. b. Give an example of a quadratic function that has a minimum value. How do you know that it has a minimum?

Homework

Integrated Algebra II- Section 5.1 Level A

Honors Algebra II- Section 5.1 Level B