Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 4 - Quadratic Functions - 4.4 Solving Quadratic Equations by the Square Root Property and Completing the Square - 4.4 Exercises - Page 349: 81

Answer

See graph

Work Step by Step

The function that we want to graph is shown below. Follow the steps outline to graph the function. $$ f(x)=\frac{1}{3}(x-5)^2-12. $$ Step 1: We first determine the direction in which the function opens: The given function opens upward because the constant $a= \frac{1}{3}$ is positive. Step 2:Determine the vertex and the equation for the axis of symmetry. The vertex is $(5,-12)$ and the equation for the axis of symmetry is $x = 5$ Step 3: Find the $y$ and $x$ intercepts. To find the $y$ intercept, set $x= 0$ to find the value of $y$. Similarly, to find the $x$ intercept, set $ y= 0$ to find the values of $x$. $$ \begin{aligned} f(0) & =\frac{1}{3}(0-5)^2-12 \\ & =\frac{1}{3}(25)-12 \\ & =\frac{25-3\cdot12}{3} \\ & =\frac{25-36}{3} \\ & =-\frac{11}{3} \\ & \approx -3.67. \end{aligned} $$ $y$-intercept: $(0,-3.67)$. Set $ y = 0$ and solve. $$ \begin{aligned} \frac{1}{3}(x-5)^2-12 & =0 \\ \frac{1}{3}(x-5)^2 & =12 \\ (x-5)^2 & =12(3) \\ (x-5)^2 & =36 \\ x-5 & = \pm \sqrt{36} \\ x & =5 \pm 6. \end{aligned} $$ Find the two separate solutions: $$ \begin{aligned} x & =5-6 \\ & =-1 \\ x & =5+6 \\ & =11. \end{aligned} $$ $x$-intercepts: $(-1,0), (11, 0)$. Step 4: Find the domain and range of the function and sketch it. Domain: All real numbers, Range: $[-12, \infty) $.
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