University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 3 - Section 3.7 - Implicit Differentiation - Exercises - Page 164: 13

Answer

$$\frac{dy}{dx}=\frac{y}{-x-\sin\Big(\frac{1}{y}\Big)+\frac{1}{y}\cos\Big(\frac{1}{y}\Big)}$$

Work Step by Step

$$y\sin\Big(\frac{1}{y}\Big)=1-xy$$ 1) Differentiate both sides of the equation with respect to $x$: $$\frac{d}{dx}\Big(y\sin\Big(\frac{1}{y}\Big)\Big)=\frac{d}{dx}(1-xy)$$ $$\frac{dy}{dx}\sin\Big(\frac{1}{y}\Big)+y\cos\Big(\frac{1}{y}\Big)\frac{d}{dx}\Big(\frac{1}{y}\Big)=0-(y+x\frac{dy}{dx})$$ $$\frac{dy}{dx}\sin\Big(\frac{1}{y}\Big)+y\cos\Big(\frac{1}{y}\Big)\Big(-\frac{1}{y^2}\Big)\frac{dy}{dx}=-x\frac{dy}{dx}-y$$ $$\frac{dy}{dx}\sin\Big(\frac{1}{y}\Big)-\frac{1}{y}\cos\Big(\frac{1}{y}\Big)\frac{dy}{dx}=-x\frac{dy}{dx}-y$$ 2) Collect all the terms with $dy/dx$ onto one side and solve for $dy/dx$: $$-x\frac{dy}{dx}-\frac{dy}{dx}\sin\Big(\frac{1}{y}\Big)+\frac{1}{y}\cos\Big(\frac{1}{y}\Big)\frac{dy}{dx}=y$$ $$\frac{dy}{dx}\Big(-x-\sin\Big(\frac{1}{y}\Big)+\frac{1}{y}\cos\Big(\frac{1}{y}\Big)\Big)=y$$ $$\frac{dy}{dx}=\frac{y}{-x-\sin\Big(\frac{1}{y}\Big)+\frac{1}{y}\cos\Big(\frac{1}{y}\Big)}$$
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