Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 3 - Applications of Differentiation - 3.6 Exercises - Page 212: 11

Answer

Graph

Work Step by Step

$$\eqalign{ & y = x + \frac{{32}}{{{x^2}}} \cr & {\text{Find the }}y{\text{ intercept, let }}x = 0 \cr & y = 0 + \frac{{32}}{{{0^2}}} \cr & {\text{No }}y{\text{ - intercept}}{\text{.}} \cr & {\text{Find the }}x{\text{ intercept, let }}y = 0 \cr & 0 = x + \frac{{32}}{{{x^2}}} \cr & - \frac{{32}}{{{x^2}}} = x \cr & {x^3} = - 32 \cr & x = - \root 3 \of {32} \cr & x{\text{ - intercept }}\left( { - \root 3 \of {32} ,0} \right) \cr & \cr & *{\text{Find the extrema}} \cr & {\text{Differentiate}} \cr & y' = \frac{d}{{dx}}\left[ {x + \frac{{32}}{{{x^2}}}} \right] \cr & y' = 1 + 32\left( { - 2{x^{ - 3}}} \right) \cr & y' = 1 - \frac{{64}}{{{x^3}}} \cr & {\text{Let }}y' = 0 \cr & 1 - \frac{{64}}{{{x^3}}} = 0 \cr & {x^3} = 64 \cr & x = 4 \cr & \cr & *{\text{Find the second derivative}} \cr & y'' = \frac{d}{{dx}}\left[ {1 - \frac{{64}}{{{x^3}}}} \right] \cr & y'' = 0 - 64\left( { - 3{x^{ - 4}}} \right) \cr & y'' = \frac{{192}}{{{x^4}}} \cr & \frac{{192}}{{{x^4}}} = 0 \cr & {\text{Evaluate }}y''\left( 4 \right) \cr & y''\left( 4 \right) = \frac{{192}}{{{{\left( 4 \right)}^4}}} > 0 \cr & {\text{Relative minimum at }}\left( {4,f\left( 4 \right)} \right) \to \left( {4,6} \right) \cr & \frac{{192}}{{{x^4}}} = 0 \cr & {\text{There are no values at which }}y'' = 0. \cr & {\text{No inflection points}}{\text{.}} \cr & \cr & {\text{*Calculate the asymptotes}} \cr & x + \frac{{32}}{{{x^2}}} \cr & x = 0 \cr & {\text{Vertical asymptotes at }}x = 0 \cr & \mathop {\lim }\limits_{x \to \infty } \left( {x + \frac{{32}}{{{x^2}}}} \right) = \infty \cr & \mathop {\lim }\limits_{x \to - \infty } \left( {x + \frac{{32}}{{{x^2}}}} \right) = - \infty \cr & {\text{No horizontal asymptotes}} \cr & \cr & {\text{Graph}} \cr} $$
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