Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 6 - Section 6.3 - Volumes by Cylindrical Shells - 6.3 Exercises - Page 465: 13

Answer

$V = \frac{{2\pi }}{3}\left( {27 - 5\sqrt 5 } \right)$

Work Step by Step

$$\eqalign{ & y = \sqrt {5 + {x^2}} {\text{, }}y = 0,{\text{ }}x = 0,{\text{ }}x = 2 \cr & {\text{Apply the shell method about the }}y{\text{ - axis}}{\text{.}} \cr & V = \int_a^b {2\pi x} f\left( x \right)dx,{\text{ where }}0 \leqslant a \leqslant b \cr & {\text{Therefore}}{\text{,}} \cr & V = \int_0^2 {2\pi x\left( {\sqrt {5 + {x^2}} } \right)} dx \cr & V = \pi \int_0^2 {2x{{\left( {5 + {x^2}} \right)}^{1/2}}dx} \cr & {\text{Integrating}} \cr & V = \pi \left[ {\frac{{{{\left( {5 + {x^2}} \right)}^{3/2}}}}{{3/2}}} \right]_0^2 \cr & V = \frac{{2\pi }}{3}\left[ {{{\left( {5 + {x^2}} \right)}^{3/2}}} \right]_0^2 \cr & {\text{Evaluating}} \cr & V = \frac{{2\pi }}{3}\left[ {{{\left( {5 + {2^2}} \right)}^{3/2}} - {{\left( {5 + {0^2}} \right)}^{3/2}}} \right] \cr & V = \frac{{2\pi }}{3}\left[ {{{\left( 9 \right)}^{3/2}} - {{\left( 5 \right)}^{3/2}}} \right] \cr & V = \frac{{2\pi }}{3}\left( {27 - 5\sqrt 5 } \right) \cr} $$
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