Thomas' Calculus 13th Edition

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

Chapter 3: Derivatives - Section 3.7 - Implicit Differentiation - Exercises 3.7 - Page 155: 13

Answer

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

Work Step by Step

$$\eqalign{ & y\sin \left( {\frac{1}{y}} \right) = 1 - xy \cr & {\text{differentiate both sides with respect to }}x \cr & \frac{d}{{dx}}\left( {y\sin \left( {\frac{1}{y}} \right)} \right) + \frac{d}{{dx}}\left( {xy} \right) = 0 \cr & \cr & {\text{Use the product rule}} \cr & y\frac{d}{{dx}}\left( {\sin \left( {\frac{1}{y}} \right)} \right) + \sin \left( {\frac{1}{y}} \right)\frac{d}{{dx}}\left( y \right) + x\frac{d}{{dx}}\left( y \right) + y\frac{d}{{dx}}\left( x \right) = 0 \cr & \cr & {\text{Find derivatives}} \cr & y\cos \left( {\frac{1}{y}} \right)\frac{d}{{dx}}\left( {\frac{1}{y}} \right) + \sin \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + x\frac{{dy}}{{dx}} + y = 0 \cr & y\cos \left( {\frac{1}{y}} \right)\left( { - \frac{1}{{{y^2}}}} \right)\frac{{dy}}{{dx}} + \sin \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + x\frac{{dy}}{{dx}} + y = 0 \cr & - \frac{1}{y}\cos \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + \sin \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + x\frac{{dy}}{{dx}} + y = 0 \cr & \cr & {\text{Solve for }}\frac{{dy}}{{dx}} \cr & - \frac{1}{y}\cos \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + \sin \left( {\frac{1}{y}} \right)\frac{{dy}}{{dx}} + x\frac{{dy}}{{dx}} = - y \cr & \left( { - \frac{1}{y}\cos \left( {\frac{1}{y}} \right) + \sin \left( {\frac{1}{y}} \right) + x} \right)\frac{{dy}}{{dx}} = - y \cr & \frac{{dy}}{{dx}} = - \frac{y}{{x - \frac{1}{y}\cos \left( {\frac{1}{y}} \right) + \sin \left( {\frac{1}{y}} \right)}} \cr} $$
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