Functions Modeling Change: A Preparation for Calculus, 5th Edition

Published by Wiley
ISBN 10: 1118583191
ISBN 13: 978-1-11858-319-7

Chapter 4 - Exponential Functions - 4.2 Comparing Exponential and Linear Functions - Exercises and Problems for Section 4.2 - Exercises and Problems - Page 155: 24

Answer

$ f(x)=22\left(\frac{23}{11} \right)^{(x+5) / 22}$

Work Step by Step

We want to have $f(x)=a b^x$. We can write $f(-5)=a b^{-5}=22$ and $f(17)=a b^{17}=46$. This gives $$ \begin{aligned} \frac{a b^{17}}{a b^{-5}} & =\frac{f(17)}{f(-5)} \\ b^{22} & =\frac{46}{22} \\ b & =\left(\frac{46}{22} \right)^{1 / 22}=\left(\frac{23}{11} \right)^{1 / 22} \end{aligned} $$ We determine $a$: $$ \begin{aligned} a b^{-5}& =22\\ a & =b^{5}\cdot 22 \\ a & =\left(\left(\frac{23}{11} \right)^{1 / 22}\right)^5\cdot 22\\ &=22\left(\frac{23}{11} \right)^{5 / 22} \end{aligned} $$ It follows that $$\begin{aligned} f(x)&=22\left(\frac{23}{11} \right)^{5 / 22}\cdot\left(\left(\frac{23}{11} \right)^{1 / 22}\right)^x\\ &=22\left(\frac{23}{11} \right)^{(x+5) / 22} \end{aligned}$$
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