Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 4 - Section 4.1 - Maximum and Minimum Values - 4.1 Exercises - Page 284: 59

Answer

The absolute maximum is $f(e^{1/2}) = \frac{1}{2e}$ The absolute minimum is $f(\frac{1}{2}) = -4~ln(2)$

Work Step by Step

$f(x) = x^{-2}~ln~x$ We can find the points when $f'(x) = 0$: $f(x) = x^{-2}~ln~x$ $f'(x) = -2x^{-3}~ln~x+x^{-3} = 0$ $ln~x = \frac{1}{2}$ $x = e^{1/2}$ We can find the value of $f(e^{1/2})$ and the values of the function at the endpoints of the interval $[\frac{1}{2}, 4]$: $f(e^{1/2}) = (e^{1/2})^{-2}~ln~(e^{1/2}) = \frac{1}{2e}$ $f(\frac{1}{2}) = (\frac{1}{2})^{-2}~ln~(1/2) = -4~ln(2)$ $f(4) = (4)^{-2}~ln~(4) = \frac{1}{16}~ln~4 \lt \frac{1}{2e}$ The absolute maximum is $f(e^{1/2}) = \frac{1}{2e}$ The absolute minimum is $f(\frac{1}{2}) = -4~ln(2)$
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