Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 2 - The Derivative - 2.7 Implicit Differentiation - Exercises Set 2.7 - Page 167: 40

Answer

$x = \frac{2}{27}$

Work Step by Step

Slope of line $x+2y-2 = 0$ is $m_{1} = -\frac{1}{2}$ So, the line perpendicular has slope $m = 2$ (negative reciprocal) Slope of curve $y^{3} = 2x^{2}$ can be obtained through implicit differentiation : $3y^{2}\frac{dy}{dx} = 4x$ $\frac{dy}{dx} = \frac{4x}{3y^{2}}$ Set $\frac{dy}{dx} = 2$ $\frac{4x}{3y^{2}} = 2$ $x = \frac{3}{2}y^{2}$ Use the value of x above in equation of curve $y^{3} = 2x^{2}$ $y^{3} = 2((\frac{3}{2})y^{2})^{2}$ $y^{3} = 2(\frac{9}{4}y^{4})$ $y^{3} = \frac{9}{2}y^{4}$ $\frac{2}{9} = y$ or $y = \frac{2}{9}$ Now as $x =\frac{3}{2}y^{2}$ Putting value of y $x = (\frac{3}{2})(\frac{2}{9})^{2}$ $x = (\frac{3}{2})(\frac{4}{81})$ $x = \frac{2}{27}$
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