University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 3 - Section 3.6 - The Chain Rule - Exercises - Page 159: 79

Answer

For $x=1$, $$(fog)'=\frac{5}{2}$$

Work Step by Step

$f(u)=u^5+1$, $u=g(x)=\sqrt x$, $x=1$ Applying the Chain Rule: $$(fog)'=f'(g(x))g'(x)=f'(u)u'$$ We have $f'(u)=(u^5+1)'=5u^4$ $u'=(\sqrt x)'=(x^{1/2})'=\frac{1}{2}x^{-1/2}=\frac{1}{2\sqrt x}$ Therefore, $$(fog)'=5u^4\times\frac{1}{2\sqrt x}=\frac{5(\sqrt x)^4}{2\sqrt x}=\frac{5x^2}{2\sqrt x}=\frac{5}{2}x^{3/2}$$ For $x=1$, $$(fog)'=\frac{5}{2}1^{3/2}=\frac{5}{2}$$
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