## Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole

# Chapter 3 - Section 3.1 - Quadratic Functions and Models - 3.1 Exercises - Page 252: 13

#### Answer

please see "step by step"

#### Work Step by Step

Rewrite f(x) in standard form, $f(x)=a(x-h)^{2}+k$, read the vertex, (h,x) For the y-intercept, calculate f(0) For the x- intercept, solve f(x) = 0 for x. If $a>0$, parabola opens up, the vertex is a minimum point, If $a<0$, parabola opens down, the vertex is a maximum. With this information (and possible additional points) sketch a graph Read the graph for range and domain. ------------------ a. factor out 3, $f(x)=3(x^{2}+2x) \quad$... complete the square $f(x)=3(x^{2}+2x+1-1)$ $f(x)=3(x+1)^{2}-3$ b. vertex: $(h,k)=(-1, -3)$, a=$+3$, opens up, the vertex is a minimum y-intercept: f(0) = $0$ x-intercepts: f(x)=0 $3x^{2}+6x=0$ $3x(x+2)=0$ x-intercepts: 0 and $-2$. c. see image (one pair of additional points, either side of the vertex). d. domain: all reals, $\mathbb{R}$ range: $[-3,\infty)$

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