Calculus with Applications (10th Edition)

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

Chapter 6 - Applications of the Derivative - 6.4 Implicit Differentiation - 6.4 Exercises - Page 336: 48

Answer

$$ xy^{a}=k $$ where $a$ and $k$ are constants. $$ \begin{aligned} \frac{d y}{d x} &=-\frac{y}{a x} \end{aligned} $$

Work Step by Step

$$ xy^{a}=k $$ where $a$ and $k$ are constants. Now, we can calculate $\frac{dy}{dx}$ by implicit differentiation, use the product rule as follows: $$ \begin{aligned} \frac{d}{d x}\left(x y^{a}\right) &=\frac{d}{d x}(k) \\ x \frac{d}{d x}\left(y^{a}\right)+y^{a}(1) &=0 \\ x\left(a y^{a-1} \frac{d y}{d x}\right)+y^{a} &=0 \\ a x y^{a-1} \frac{d y}{d x} &=-y^{a} \\ \frac{d y}{d x} &=-\frac{y^{a}}{a x y^{a-1}} \\ \frac{d y}{d x} &=-\frac{y}{a x} . \end{aligned} $$
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