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: 84

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. $$ g(x)=\frac{3}{4}(x+8)^2-27. $$ Step 1: We first determine the direction in which the function opens: The given function opens upward because the constant $a= \frac{3}{4}$ is positive. Step 2: Determine the vertex and the equation for the axis of symmetry. The vertex is $(-8,-27)$ and the equation for the axis of symmetry is $x = -8$. 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 $x$. $$ \begin{aligned} g(0) & =\frac{3}{4}(0+8)^2-27 \\ & =\frac{3}{4}(64)-\frac{27 \cdot 4}{4} \\ & =3(16)-27 \\ & =21 \end{aligned} $$ $y$-intercept: $(0,21)$. Set $ y = 0$ and solve. $$ \begin{aligned} \frac{3}{4}(x+8)^2-27 & =0 \\ \frac{3}{4}(x+8)^2 & =27 \\ (x+8)^2 & =27 \cdot \frac{4}{3} \\ (x+8)^2 & =36 \\ x+8 & = \pm \sqrt{36} \\ x & =-8 \pm 6. \end{aligned} $$ Find the two separate solutions: $$ \begin{aligned} x & =-8-6 \\ & =-14 \\ x & =-8+6 \\ & =-2. \end{aligned} $$ $x$-intercepts: $(-14,0), (-2, 0)$. Step 4: Find the domain and range of the function and sketch it. Domain: All real numbers, Range: $[-27, \infty) $. The graph of the parabola is shown in the figure below.
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