University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 3 - Section 3.8 - Derivatives of Inverse Functions and Logarithms - Exercises - Page 175: 64

Answer

$$\frac{dy}{dx}=\frac{y(1-xe^{x+y})}{x(ye^{x+y}-1)}$$

Work Step by Step

$$\ln xy=e^{x+y}$$ We have $$(\ln x)'=\frac{1}{x}$$ $$(e^{x})'=e^x$$ Carrying out implicit differentiation on both sides, we have $$\frac{1}{xy}\frac{d}{dx}(xy)=e^{x+y}\frac{d}{dx}(x+y)$$ $$\frac{y+x\frac{dy}{dx}}{xy}=e^{x+y}(1+\frac{dy}{dx})$$ $$\frac{1}{x}+\frac{1}{y}\frac{dy}{dx}=e^{x+y}+e^{x+y}\frac{dy}{dx}$$ $$e^{x+y}\frac{dy}{dx}-\frac{1}{y}\frac{dy}{dx}=\frac{1}{x}-e^{x+y}$$ $$\Big(e^{x+y}-\frac{1}{y}\Big)\frac{dy}{dx}=\frac{1}{x}-e^{x+y}$$ $$\frac{dy}{dx}=\frac{\frac{1}{x}-e^{x+y}}{e^{x+y}-\frac{1}{y}}=\frac{\frac{1-xe^{x+y}}{x}}{\frac{ye^{x+y}-1}{y}}$$ $$\frac{dy}{dx}=\frac{y(1-xe^{x+y})}{x(ye^{x+y}-1)}$$
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