Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 6: Applications of Definite Integrals - Section 6.1 - Volumes Using Cross-Sections - Exercises 6.1 - Page 323: 46

Answer

$\frac{3\pi}{5}$

Work Step by Step

Step 1. Draw a diagram as shown in the figure. The limits of integration with respect to $x$ can be found as from $-1$ to $0$. Step 2. Approximate using cylinders; we have $dV=2\pi (x+2)(-x^3-0)) dx=-2\pi (x^4+2x^3)\ dx$ Step 3. We have $V=-2\pi\int_{-1}^0 (x^4+2x^3)\ dx=-2\pi (\frac{1}{5}x^5+\frac{1}{2}x^4)|_{-1}^0 =2\pi (\frac{1}{5}(-1)^5+\frac{1}{2}(-1)^4)=\frac{3\pi}{5}$
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