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: 77

Answer

\[y=-9x+35\]

Work Step by Step

\[\begin{align} & y=\frac{{{\left( {{x}^{2}}-1 \right)}^{2}}}{{{x}^{3}}-6x-1} \\ & \text{Differentiate} \\ & \frac{dy}{dx}=\frac{d}{dx}\left[ \frac{{{\left( {{x}^{2}}-1 \right)}^{2}}}{{{x}^{3}}-6x-1} \right] \\ & \frac{dy}{dx}=\frac{\left( {{x}^{3}}-6x-1 \right)\frac{d}{dx}\left[ {{\left( {{x}^{2}}-1 \right)}^{2}} \right]-{{\left( {{x}^{2}}-1 \right)}^{2}}\frac{d}{dx}\left[ {{x}^{3}}-6x-1 \right]}{{{\left( {{x}^{3}}-6x-1 \right)}^{2}}} \\ & \frac{dy}{dx}=\frac{\left( {{x}^{3}}-6x-1 \right)\left[ 2\left( {{x}^{2}}-1 \right)\left( 2x \right) \right]-{{\left( {{x}^{2}}-1 \right)}^{2}}\left( 3{{x}^{2}}-6 \right)}{{{\left( {{x}^{3}}-6x-1 \right)}^{2}}} \\ & \frac{dy}{dx}=\frac{4x\left( {{x}^{2}}-1 \right)\left( {{x}^{3}}-6x-1 \right)-\left( 3{{x}^{2}}-6 \right){{\left( {{x}^{2}}-1 \right)}^{2}}}{{{\left( {{x}^{3}}-6x-1 \right)}^{2}}} \\ & \text{Calculate the derivative at the point }\left( 3,8 \right) \\ & {{\left. \frac{dy}{dx} \right|}_{x=3}}=\frac{4\left( 3 \right)\left( {{3}^{2}}-1 \right)\left( {{3}^{3}}-6\left( 3 \right)-1 \right)-\left( 3{{\left( 3 \right)}^{2}}-6 \right){{\left( {{3}^{2}}-1 \right)}^{2}}}{{{\left( {{3}^{3}}-6\left( 3 \right)-1 \right)}^{2}}} \\ & \text{Simplifying} \\ & {{\left. \frac{dy}{dx} \right|}_{x=3}}=\frac{4\left( 3 \right)\left( 8 \right)\left( 8 \right)-\left( 27-6 \right){{\left( 8 \right)}^{2}}}{{{\left( 8 \right)}^{2}}} \\ & {{\left. \frac{dy}{dx} \right|}_{x=3}}=-9 \\ & m=-9 \\ & \text{Find the equation of the tangent line at the point }\left( 3,8 \right) \\ & y-{{y}_{1}}=m\left( x-{{x}_{1}} \right) \\ & y-8=-9\left( x-3 \right) \\ & y-8=-9x+27 \\ & \text{ }y=-9x+35 \\ & \text{Graph} \\ \end{align}\]
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