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: 9

Answer

Graph

Work Step by Step

$$\eqalign{ & y = \frac{{3x}}{{{x^2} - 1}} \cr & {\text{Find the }}y{\text{ intercept, let }}x = 0 \cr & y = \frac{{3\left( 0 \right)}}{{{{\left( 0 \right)}^2} - 1}} \cr & y = 0 \cr & y{\text{ - intercept }}\left( {0,0} \right) \cr & {\text{Find the }}x{\text{ intercept, let }}y = 0 \cr & 0 = \frac{{3x}}{{{x^2} - 1}} \cr & x = 0 \cr & x{\text{ - intercept }}\left( {0,0} \right) \cr & \cr & *{\text{Find the extrema}} \cr & {\text{Differentiate}} \cr & y' = \frac{d}{{dx}}\left[ {\frac{{3x}}{{{x^2} - 1}}} \right] \cr & y' = \frac{{\left( {{x^2} - 1} \right)\left( 3 \right) - 3x\left( {2x} \right)}}{{{{\left( {{x^2} - 1} \right)}^2}}} \cr & y' = \frac{{3{x^2} - 3 - 6{x^2}}}{{{{\left( {{x^2} - 1} \right)}^2}}} \cr & y' = \frac{{ - 3{x^2} - 3}}{{{{\left( {{x^2} - 1} \right)}^2}}} \cr & {\text{Let }}y' = 0 \cr & - 3{x^2} - 3 = 0 \cr & 3{x^2} + 3 = 0,{\text{ There are no values at which }}y' = 0, \cr & {\text{No relative extrema}}{\text{.}} \cr & \cr & {\text{Find the second derivative}} \cr & y'' = \frac{d}{{dx}}\left[ {\frac{{ - 3{x^2} - 3}}{{{{\left( {{x^2} - 1} \right)}^2}}}} \right] \cr & y'' = \frac{{{{\left( {{x^2} - 1} \right)}^2}\left( { - 6x} \right) - \left( { - 3{x^2} - 3} \right)\left( 2 \right)\left( {{x^2} - 1} \right)\left( {2x} \right)}}{{{{\left( {{x^2} - 1} \right)}^4}}} \cr & y'' = \frac{{6x\left( {{x^2} + 3} \right)}}{{{{\left( {{x^2} - 1} \right)}^4}}} \cr & \cr & *{\text{Find the Inflection points}} \cr & y'' = \frac{{6x\left( {{x^2} + 3} \right)}}{{{{\left( {{x^2} - 1} \right)}^4}}} \cr & \frac{{6x\left( {{x^2} + 3} \right)}}{{{{\left( {{x^2} - 1} \right)}^4}}} = 0 \cr & x = 0 \cr & {\text{Inflection point at }}x = 0 \cr & y\left( 0 \right) = \frac{{3\left( 0 \right)}}{{{{\left( 0 \right)}^2} - 1}} = 0,{\text{ }}\left( {0,0} \right) \cr & \cr & {\text{*Calculate the asymptotes}} \cr & y = \frac{{3x}}{{{x^2} - 1}} \cr & {x^2} - 1 = 0,{\text{ }}x = \pm 1 \cr & {\text{Vertical asymptotes, }}x = 1,{\text{ }}x = - 1 \cr & \mathop {\lim }\limits_{x \to \infty } \left( {\frac{{3x}}{{{x^2} - 1}}} \right) = 0 \cr & \mathop {\lim }\limits_{x \to - \infty } \left( {\frac{{3x}}{{{x^2} - 1}}} \right) = 0 \cr & {\text{Horizontal asymptote }}y = 0 \cr & \cr & {\text{Graph}} \cr} $$
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