Calculus Concepts: An Informal Approach to the Mathematics of Change 5th Edition

Published by Brooks Cole
ISBN 10: 1-43904-957-2
ISBN 13: 978-1-43904-957-0

Chapter 3 - Determining Change: Derivatives - 3.4 Activities - Page 224: 16

Answer

inside: $g(x)=x^{2}+5 x$ outside: $f(g)=g^{1/3}$ derivative: $f^{\prime}(x)=\dfrac{1}{3}(x^{2}+5 x)^{-2/3} (2x+5)$

Work Step by Step

Given $$f(x)=\sqrt[3]{x^{2}+5 x}$$ Rewriting $f(x)$ as $$f(x)= (x^{2}+5 x)^{1/3}$$ Use the chain rule to take the derivative $$ \frac{d f(g(x))}{d x}=f^{\prime}(g(x)) g^{\prime}(x) $$ Here $g(x)=x^{2}+5 x$ and $f(g)=g^{1/3},$ then \begin{align*} f'(x) &=\left(g^{1/3}(x)\right)^{\prime}\\ &=\frac{1}{3}g^{-2/3}(x) g^{\prime}(x)\\ &=\frac{1}{3}(x^{2}+5 x)^{-2/3} (2x+5) \end{align*}
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