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 - 3.5 Exercises - Page 203: 64

Answer

Graph

Work Step by Step

$$\eqalign{ & y = \frac{{2{x^2}}}{{{x^2} - 4}} \cr & {\text{Find the }}y{\text{ intercept, let }}x = 0 \cr & y = \frac{{2{{\left( 0 \right)}^2}}}{{{{\left( 0 \right)}^2} - 4}} \to y = 0 \cr & y{\text{ - intercept }}\left( {0,0} \right) \cr & {\text{Find the }}x{\text{ intercept, let }}y = 0 \cr & 0 = \frac{{2{x^2}}}{{{x^2} - 4}} \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{{2{x^2}}}{{{x^2} - 4}}} \right] \cr & y' = \frac{{\left( {{x^2} - 4} \right)\left( {4x} \right) - 2{x^2}\left( {2x} \right)}}{{{{\left( {{x^2} - 4} \right)}^2}}} \cr & y' = \frac{{4{x^3} - 16x - 4{x^4}}}{{{{\left( {{x^2} - 4} \right)}^2}}} \cr & y' = \frac{{ - 16x}}{{{{\left( {{x^2} - 4} \right)}^2}}} \cr & {\text{Let }}y' = 0 \cr & - 16x = 0 \cr & x = 0 \cr & {\text{Evaluate }}y'\left( { - 1} \right){\text{ and }}y'\left( 1 \right) \cr & y\left( { - 1} \right)' = \frac{{ - 16\left( { - 1} \right)}}{{{{\left( {{{\left( { - 1} \right)}^2} - 4} \right)}^2}}} > 0 \cr & y\left( 1 \right)' = \frac{{ - 16\left( 1 \right)}}{{{{\left( {{{\left( 1 \right)}^2} - 4} \right)}^2}}} < 0 \cr & y\left( { - 1} \right)' > 0,{\text{ }}y\left( 0 \right)' = 0,{\text{ }}y\left( 1 \right)' < 0 \cr & {\text{Then, there is a relative maximum at }}x = 0 \cr & y\left( 0 \right) = \frac{{2{{\left( 0 \right)}^2}}}{{{{\left( 0 \right)}^2} - 4}} = 0 \cr & {\text{Relative maximum at }}\left( {0,0} \right) \cr & \cr & {\text{*Calculate the asymptotes}} \cr & \frac{{x + 1}}{{{x^2} - 4}} \cr & {x^2} - 4 = 0 \to x = \pm 2 \cr & {\text{Vertical asymptotes at }}x = \pm 2 \cr & \mathop {\lim }\limits_{x \to \infty } \frac{{2{x^2}}}{{{x^2} - 4}} = 2 \cr & \mathop {\lim }\limits_{x \to - \infty } \frac{{2{x^2}}}{{{x^2} - 4}} = 2 \cr & {\text{Horizontal asymptote }}y = 2 \cr & \cr & {\text{*Symmetry}} \cr & f\left( { - x} \right) = \frac{{2{{\left( { - x} \right)}^2}}}{{{{\left( { - x} \right)}^2} - 4}} = \frac{{2{x^2}}}{{{x^2} - 4}} \cr & f\left( { - x} \right) = f\left( x \right){\text{ The function is even}} \cr & {\text{Symmetry about the }}y{\text{ - axis}} \cr & \cr & {\text{Graph}} \cr} $$
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