Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 3 - Section 3.4 - The Chain Rule - 3.4 Exercises - Page 206: 2

Answer

$\frac{dy}{dx}=\frac{3x^2}{2\sqrt{x^3+2}}$

Work Step by Step

Considering $u=x^3+2$, the function can be written as $y=\sqrt{u}$ or $y=u^{1/2}$. We have the composite function $y=f(g(x))$ where $g(x)=x^3+2$ and $f(u)=u^{1/2}$. Find $dy/du$: $\frac{dy}{du}=\frac{d}{du}(u^{1/2})=\frac{1}{2}u^{-1/2}=\frac{1}{2\sqrt{u}}$ Find $du/dx$: $\frac{du}{dx}=\frac{d}{dx}(x^3+2)=3x^2+0=3x^2$ Find $dy/dx$ using the chain rule: $\frac{dy}{dx}=\frac{dy}{du}\cdot \frac{du}{dx}=\frac{1}{2\sqrt{u}}\cdot 3x^2=\frac{1}{2\sqrt{x^3+2}}\cdot 3x^2=\frac{3x^2}{2\sqrt{x^3+2}}$ Thus, $\frac{dy}{dx}=\frac{3x^2}{2\sqrt{x^3+2}}$
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