Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 3 - Applications of Differentiation - Review - Exercises - Page 286: 3

Answer

$$ f(x)=\frac{3 x-4}{x^{2}+1}, \quad [-2,2], $$ The local minimum valuei s $$ f\left(-\frac{1}{3}\right)=\frac{-5}{10 / 9}=-\frac{9}{2} $$ is a local minimum value. Checking the endpoints, we find $$ f(-2)=-2 \text { and } f(2)=\frac{2}{5} . $$ Thus, $$ f\left(-\frac{1}{3}\right)=-\frac{9}{2} $$ is the absolute minimum value and $$ f(2)=\frac{2}{5} $$ is the absolute maximum value

Work Step by Step

$$ f(x)=\frac{3 x-4}{x^{2}+1}, \quad [-2,2], $$ Since $ f$ is continuous on [-2,2],we can use the Closed Interval Method $$ f(x)=\frac{3 x-4}{x^{2}+1} $$ $$ \begin{aligned} f^{\prime}(x) &=\frac{\left(x^{2}+1\right)(3)-(3 x-4)(2 x)}{\left(x^{2}+1\right)^{2}} \\ & =\frac{-\left(3 x^{2}-8 x-3\right)}{\left(x^{2}+1\right)^{2}} \\ &=\frac{-(3 x+1)(x-3)}{\left(x^{2}+1\right)^{2}} \end{aligned} $$ Since $f^{\prime}(x)$ exists for all $x$ the only critical numbers of $f$ occur when $f^{\prime}(x)=0$ that is, $$ x=-\frac{1}{3} \text { or } x=3 $$ but $3$ is not in the interval. For $-\frac{1}{3}0 $$ For $ -2
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