Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 3: Derivatives - Section 3.6 - The Chain Rule - Exercises 3.6 - Page 149: 73

Answer

a. $\frac{2}{3}$ b. $2\pi+5$ c. $15-8\pi$ d. $\frac{37}{6}$ e. $-1$ f. $\frac{\sqrt 2}{24}$ g. $\frac{5}{32}$ h. $\frac{-5}{3\sqrt 17}$

Work Step by Step

a. let $y$ = $2f(x)$ $y'$ = $2f'(x)$ $2f'(2)$ = $(2)(\frac{1}{3})$ = $\frac{2}{3}$ b. let $y$ = $f(x)+g(x)$ $y'$ = $f'(x)+g'(x)$ $f'(3)+g'(3)$ = $2\pi+5$ c. let $y$ = $f(x)$$g(x)$ $y'$ = $f(x)g'(x)+g(x)f'(x)$ $f(3)g'(3)+g(3)f'(3)$ = $(3)(5)+(-4)(2\pi)$ = $15-8\pi$ d. let y = $\frac{f(x)}{g(x)}$ $y'$ = $\frac{g(x)f'(x)-f(x)g'(x)}{g^{2}(x)}$ $\frac{g(2)f'(2)-f(2)g'(2)}{g^{2}(2)}$ = $\frac{(2)(\frac{1}{3})-(8)(-3)}{(2)^{2}}$ = $\frac{74}{12}$ = $\frac{37}{6}$ e. let $y$ = $f(g(x))$ $y'$ = $f'(g(x))g'(x)$ $f'(g(x))g'(x)$ = $f'(g(2))g'(2)$ = $f'(2)[-3]$ = $(\frac{1}{3})(-3)$ = $-1$ f. let $y$ = $\sqrt {f(x)}$ $y'$ = $\frac{1}{2\sqrt {f(x)}}f'(x)$ $\frac{1}{2\sqrt {f(x)}}f'(x)$ = $\frac{1}{2\sqrt {8}}(\frac{1}{3})$ = $\frac{1}{12\sqrt 2}$ = $\frac{\sqrt 2}{24}$ g. let $y$ = $\frac{1}{g^{2}(x)}$ $y'$ = $\frac{-2g(x)g'(x)}{g^{3}(x)}$ $\frac{-2g'(x)}{g^{3}(x)}$ = $\frac{-2g'(3)}{g^{3}(3)}$ = $\frac{-2(5)}{(-4)^{3}}$ = $\frac{5}{32}$ h. let $y$ = $\sqrt {f^{2}(x)+g^{2}(x)}$ $y'$ = $\frac{2f(x)f'(x)+2g(x)g'(x)}{2\sqrt {f^{2}(x)+g^{2}(x)}}$ = $\frac{f(x)f'(x)+g(x)g'(x)}{\sqrt {f^{2}(x)+g^{2}(x)}}$ $\frac{f(x)f'(x)+g(x)g'(x)}{\sqrt {f^{2}(x)+g^{2}(x)}}$ = $\frac{f(2)f'(2)+g(2)g'(2)}{\sqrt {f^{2}(2)+g^{2}(2)}}$ = $\frac{(8)(\frac{1}{3})+(2)(-3)}{\sqrt {(8)^{2}+(2)^{2}}}$ = $\frac{-5}{3\sqrt 17}$
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