Big Ideas Math Algebra 1, 2015
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Big Ideas Math Algebra 1, 2015 View details
5. Using Intercept Form
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Exercise 10 Page 455

The x-intercepts occur at the points where the graph intercepts the x-axis. The axis of symmetry is the vertical line located halfway between these points.

Graph:

Domain: All real numbers
Range: y ≤ 16

Practice makes perfect

To draw the graph of the given function, we will follow four steps.

  1. Identify and plot the x-intercepts.
  2. Find and graph the axis of symmetry.
  3. Find and plot the vertex.
  4. Draw the parabola through the vertex and the points where the x-intercepts occur.

Let's go through these steps one at a time.

Identify and Plot the x-intercepts

Let's start by recalling the intercept form of a quadratic function. f(x)=a(x-p)(x-q)

In this form, where a ≠ 0, the x-intercepts are p and q. Let's consider the given function. h(x)= - 4(x- 7)(x- 3) We can see that a= - 4, p= 7, and q= 3. Therefore, the x-intercepts occur at ( 7,0) and ( 3,0).

Find and Graph the Axis of Symmetry

The axis of symmetry is halfway between (p,0) and (q,0). Since we know that p=7 and q=3, the axis of symmetry of our parabola is halfway between (7,0) and (3,0). x=p+q/2 ⇒ x=7+ 3/2=10/2=5 We found that the axis of symmetry is the vertical line x=5.

Find and Plot the Vertex

Since the vertex lies on the axis of symmetry, its x-coordinate is 5. To find the y-coordinate, we will substitute 5 for x in the given equation.
h(x)=- 4(x-7)(x-3)
h( 5)=- 4( 5-7)( 5-3)
â–Ľ
Simplify right-hand side
h(5)=- 4(- 2)(2)
h(5)=8(2)
h(5)=16
The y-coordinate of the vertex is 16. Therefore, the vertex is the point (5,16).

Draw the Parabola

Finally, we will draw the parabola as a curve passing through the vertex and the x-intercepts.

We can see that there are no restrictions on the x-variable. Furthermore, h(x) — or y — takes values less than or equal to 16. We can write the domain and range of the function using this information. Domain:& All real numbers Range:& y ≤ 16