Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 1 - Review Exercises - Page 303: 106

Answer

$f\left( g\left( x \right) \right)$ and $g\left( f\left( x \right) \right)$ of the function $f\left( x \right)=\frac{3}{5}x+\frac{1}{2}$ and $g\left( x \right)=\frac{5}{3}x-2$ is $f\left( g\left( x \right) \right)=x-\frac{7}{10}\text{ and }g\left( f\left( x \right) \right)=x-\frac{7}{6}$ respectively, and f and g are not inverses of each other.

Work Step by Step

Now, consider the function: $\begin{align} & f\left( g\left( x \right) \right)=f\left( \frac{5}{3}x-2 \right) \\ & =\frac{3}{5}\left( \frac{5}{3}x-2 \right)+\frac{1}{2} \\ & =\frac{15}{15}x-\frac{6}{5}+\frac{1}{2} \\ & =x-\frac{12-5}{10} \end{align}$ That is, $\begin{align} & f\left( g\left( x \right) \right)=x-\frac{12-5}{10} \\ & =x-\frac{7}{10} \end{align}$ Next considering $\begin{align} & g\left( f\left( x \right) \right)=g\left( \frac{3}{5}x+\frac{1}{2} \right) \\ & =\frac{5}{3}\left( \frac{3}{5}x+\frac{1}{2} \right)-2 \\ & =x+\frac{5}{6}-2 \\ & =x-\frac{7}{6} \end{align}$ This shows that the functions $f$ and $g$ are not inverses of each other, since none of the compositions resulted in x. Hence, $f\left( g\left( x \right) \right)$ and $g\left( f\left( x \right) \right)$ of the function $f\left( x \right)=\frac{3}{5}x+\frac{1}{2}$ and $g\left( x \right)=\frac{5}{3}x-2$ is $f\left( g\left( x \right) \right)=x-\frac{7}{10}\text{ and }g\left( f\left( x \right) \right)=x-\frac{7}{6}$ respectively, and f and g are not inverses of each other.
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