Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 3 - Derivatives - 3.7 The Chain Rule - 3.7 Exercises - Page 192: 78

Answer

\[y=\frac{3}{2}x+\frac{1}{2}\text{ and }y=-3x-8\text{ }\]

Work Step by Step

\[\begin{align} & y=x\sqrt{5-{{x}^{2}}} \\ & \text{Differentiate} \\ & \frac{dy}{dx}=\frac{d}{dx}\left[ x\sqrt{5-{{x}^{2}}} \right] \\ & \frac{dy}{dx}=x\frac{d}{dx}\left[ \sqrt{5-{{x}^{2}}} \right]+\sqrt{5-{{x}^{2}}}\frac{d}{dx}\left[ x \right] \\ & \frac{dy}{dx}=x\left( \frac{-2x}{2\sqrt{5-{{x}^{2}}}} \right)+\sqrt{5-{{x}^{2}}}\left( 1 \right) \\ & \frac{dy}{dx}=\sqrt{5-{{x}^{2}}}-\frac{{{x}^{2}}}{\sqrt{5-{{x}^{2}}}} \\ & \text{Calculate the derivative at the point }\left( 1,2 \right)\text{ and }\left( -2,-2 \right) \\ & {{\left. \frac{dy}{dx} \right|}_{x=1}}=\sqrt{5-{{\left( 1 \right)}^{2}}}-\frac{{{\left( 1 \right)}^{2}}}{\sqrt{5-{{\left( 1 \right)}^{2}}}}=\frac{3}{2} \\ & {{\left. \frac{dy}{dx} \right|}_{x=-2}}=\sqrt{5-{{\left( -2 \right)}^{2}}}-\frac{{{\left( -2 \right)}^{2}}}{\sqrt{5-{{\left( -2 \right)}^{2}}}}=-3 \\ & \text{Find the equation of the tangent line at the point }\left( 1,2 \right)\text{ } \\ & \text{and }\left( -2,-2 \right) \\ & y-{{y}_{1}}=m\left( x-{{x}_{1}} \right) \\ & y-2=\frac{3}{2}\left( x-1 \right) \\ & y-2=\frac{3}{2}x-\frac{3}{2} \\ & \text{ }y=\frac{3}{2}x+\frac{1}{2} \\ & and \\ & y-{{y}_{1}}=m\left( x-{{x}_{1}} \right) \\ & y+2=-3\left( x+2 \right) \\ & y+2=-3x-6 \\ & \text{ }y=-3x-8 \\ & \text{Graph} \\ \end{align}\]
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