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: 100

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. $$ \begin{aligned} d(m) &= 0.25\left(m-18\right)^2-68. \end{aligned} $$ Step 1: We first determine the direction in which the function opens: The given function opens upward because the constant $a= 0.25$ is positive. Step 2: Determine the vertex and the equation for the axis of symmetry. The vertex is $(18,-68)$ and the equation for the axis of symmetry is $x = 18$. 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 $x$. $$ \begin{aligned} d(0)& =0.25\left(0-18\right)^2-68\\ &= 13\\ &\text{y-intercept: (0,13)}. \end{aligned} $$ Set $ d = 0$ and solve. $$ \begin{aligned} 0.25\left(m-18\right)^2-68& =0\\ \left(m-18\right)^2&= \frac{68}{0.25} \\ m-18& = \pm\sqrt{272}\\ m&= 18\pm \sqrt{272} \end{aligned} $$ Find the two separate solutions: $$ \begin{aligned} m&=18+ \sqrt{272}\\ &= 34.49 \\ \textbf{or}\\ m&= 18-\sqrt{272}\\ & = 1.51 \end{aligned} $$ $x$-intercept: $(1.51,0), (34.49 , 0)$. Step 4: Find the domain and range of the function and sketch it. Domain: All real numbers, Range: $[-68, \infty) $.
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