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: 25

Answer

B) $ f(x)=2.23\cdot(1.032)^x $

Work Step by Step

A) We know that a function is linear if the differences of successive values of the function is a constant. A function is exponential if the ratios of successive values of the function is a constant. $$ \begin{aligned} & f(3)-f(0)=2.45-2.23=0.22\\ & f(6)-f(3)=2.7-2.45=0.47 \end{aligned} $$ The function is not linear. The function $h$, is linear for the same reason. $$ \begin{aligned} & \frac{f(3)}{f(0)}=\frac{2.45}{2.23}=1.1 \\ & \frac{f(6)}{f(3)}=\frac{2.7}{2.45}=1.1 \end{aligned} $$ Hence, the function is exponential. B) We want to have $f(x)=a b^x$. The table shows that the points $(0,2.23),(3,2.45)$ lie on the curve of $f(x)$. We must have $f(0)=a b^0=a=2.23$ and so $f(x)=2.23 b^x$. $f(3)=2.23 b^3=2.45 \Longrightarrow b=(2.45/2.23)^{1 / 3}=1.032$ Hence: $$ f(x)=2.23\cdot(1.032)^x $$
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