Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 5 - Applications Of The Definite Integral In Geometry, Science, And Engineering - 5.3 Volumes By Cylindrical Shells - Exercises set 5.3 - Page 371: 27

Answer

$\text{The volume is}$ \begin{align} V =\frac{7\pi}{4} \end{align}

Work Step by Step

$\text{It is given that}$ \begin{align} y = \frac{1}{x^3}; \ x = 1; \ x = 2 \ \ and \ \ y = 0 \end{align} $\text{The given region is revolved about x = -1. Meaning that the cross }$ $\text{section generates a cylindircal surface of height $\frac{1}{x^3}$ and radius (x+1).}$ $\text{Thus, the volume is}$ \begin{align} V = 2\pi \int_1^2 \frac{1}{x^3}(x+1) \ dx = 2\pi \left[-\frac{1}{x} - \frac{1}{2x^2} \right]_1^2 = 2\pi \times \frac{7}{8} = \frac{7\pi}{4} \end{align}
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