Finite Math and Applied Calculus (6th Edition)

Published by Brooks Cole
ISBN 10: 1133607705
ISBN 13: 978-1-13360-770-0

Chapter 9 - Section 9.2 - Exponential Functions and Models - Exercises - Page 644: 73a

Answer

Linear model: $\qquad F =65t-60$ Exponential model: $\qquad F= 97.2(1.20)^{t}$ The exponential model is more appropriate.

Work Step by Step

A linear model has the form: $F=mt+b$ Given the points: $(4,200)$ and $(10,590)$, we find the slope: $m=\displaystyle \frac{F_{2}-F_{1}}{t_{2}-t_{1}}=\frac{590-200}{10-4}=65$ So, $F=65t+b$ To find b, insert $(t=4,F=200)$ $b=200-(65)(4)=-60$ Linear model: $\qquad F =65t-60$ The differences of successive terms in the table are not constant. They are increasing, so our linear model will not be a good fit. Exponential models have the form: $F=Ab^{t}$ Substitute $(t=4,F=200)\qquad 200=Ab^{4},$ substitute $(t=10,F=590)\qquad 590=Ab^{10}.$ Divide the second equation by the first: $\displaystyle \begin{aligned}\frac{590}{200}&=\displaystyle \frac{b^{10}}{b^{4}}=b^{6}\\2.95&=b^{6}\displaystyle \\b&=(2.95)^{16}\displaystyle \approx 1.19758\approx 1.20\end{aligned}$ Substitute the value of $b$ in $200=Ab^{4}$ $\displaystyle \begin{aligned}200&\displaystyle \approx A(1.19758)^{4}\approx 2.0569A,\text{so}\\A&\displaystyle \approx\frac{200}{2.0569}\approx 97.2\end{aligned}$ Exponential model: $\qquad F= 97.2(1.20)^{t}$ The successive ratios of the values of $F$ in the table are roughly $(1.20)^{2}\approx 1.44$, and, knowing $F(0)$, we would multiply it with $1.20$ to obtain $F(1)$, and then again with $1.20$ to obtain $F(2)$ so, $F(2)\approx 100(1.20)^{2}\approx 97.2(1.20)^{2}$. Thus, we will take the exponential model to be more appropriate.
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