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 6.4 - Areas of Surfaces of Revolution - Exercises 6.4 - Page 341: 21

Answer

$S$ = $\pi(\frac{15}{16}+\ln2)$

Work Step by Step

$\frac{dx}{dy}$ = $\frac{1}{2}$$(e^{y}-e^{-y})$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$2\pi(x)(\sqrt {1+(\frac{dx}{dy})^{2}}$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$2\pi(\frac{1}{2})(e^{y}+e^{-y})(\sqrt {1+(\frac{1}{2}(e^{y}-e^{-y}))^{2}}$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$\pi(e^{y}+e^{-y})(\sqrt {1+\frac{1}{4}e^{2y}-\frac{1}{2}+\frac{1}{4}e^{-2y}}$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$\pi(e^{y}+e^{-y})(\sqrt {\frac{1}{4}e^{2y}+\frac{1}{2}+\frac{1}{4}e^{-2y}}$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$\pi(e^{y}+e^{-y})(\sqrt {(\frac{1}{2}(e^{y}+e^{-y}))^{2}}$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$\pi(e^{y}+e^{-y})\frac{1}{2}(e^{y}+e^{-y})$$dy$ $S$ = $\int_{{\,0}}^{{\,\ln2}}$$\frac{\pi}{2}(e^{2y}+2+e^{-2y})$$dy$ $S$ = $\frac{\pi}{2}(\frac{1}{2}e^{2y}+2y-\frac{1}{2}e^{-2y})$$|_{{\,0}}^{{\,\ln2}}$ $S$ = $\frac{\pi}{2}[(2+2\ln2-\frac{1}{8})-(\frac{1}{2}+0-\frac{1}{2})]$ $S$ = $\pi(\frac{15}{16}+\ln2)$
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