Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 6 - Applications of the Derivative - 6.5 Related Rates - 6.5 Exercises - Page 341: 7

Answer

$$ xe^{y}=2-\ln2+\ln x; \quad [x=2 , \quad y=0 , \quad \frac{dx}{dt}=6] $$ $$ \frac{d y}{d t}=-\frac{3}{2} $$

Work Step by Step

$$ xe^{y}=2-\ln2+\ln x; \quad [x=2 , \quad y=0 , \quad \frac{dx}{dt}=6] $$ Now, we can calculate $\frac{dy}{dt}$ by implicit differentiation, use the product rule as follows: $$ \begin{aligned} e^{y} \frac{d x}{d t}+x e^{y} \frac{d y}{d t} &=0+\frac{1}{x} \frac{d x}{d t} \\ x e^{y} \frac{d y}{d t} &=\left(\frac{1}{x}-e^{y}\right) \frac{d x}{d t} \\ \frac{d y}{d t} &=\frac{\left(\frac{1}{x}-e^{y}\right) \frac{d x}{d t}}{x e^{y}} \\ &=\frac{\left(1-x e^{y}\right) \frac{d x}{d t}}{x^{2} e^{y}} \\ & \quad \text { subistituting } \left[\begin{array}{c}{x=2 , \quad y=0 , \quad \frac{dx}{dt}=6 } \end{array}\right] , \\ &=\frac{\left[1-(2) e^{0}\right](6)}{2^{2} e^{0}} \\ &=\frac{-6}{4} \\ &=-\frac{3}{2} . \end{aligned} $$
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