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 - Review Exercises and Problems for Chapter Four - Page 177: 23

Answer

$ g(x)=14.20(0.6024)^x $

Work Step by Step

We want to find $f(x)=ab^x$,given $g(1.7)=6$ and $g(2.5)=4$. We now find $b$ and $a$. $$ \begin{aligned} \frac{a b^{2.5}}{a b^{1.7}} & =\frac{4}{6}=\frac{g(2.5)}{g(1.7)} \\ b^{0.8} & =\frac{4}{6}=\frac{2}{3} \\ b & =\left(\frac{2}{3}\right)^{\frac{1}{0.8}}=\left(\frac{2}{3}\right)^{5/4}\approx 0.6024. \end{aligned} $$ and $$ \begin{aligned} g(1.7) & =a\left(\left(\frac{2}{3}\right)^{5/4}\right)^{1.7}=6 \\ a & =\frac{6}{\left(\frac{2}{3}\right)^{17/8}} \\ & \approx 14.20 . \end{aligned} $$ Hence $$ g(x)=14.20(0.6024)^x $$
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