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 340: 13

Answer

$\dfrac{98 \pi}{81}$

Work Step by Step

Integrate the integral to calculate the surface area as follows: We have: $S_{A}= (2 \pi)\int_{a}^{b} y \sqrt {1+(\dfrac{dy}{dx})^2}$ or, $ =(2 \pi)\int_{0}^{2}(\dfrac{x^3}{9}) \cdot \sqrt {1+(\dfrac{x}{3})^2} dx$ or, $= \dfrac{2 \pi}{27} \int_0^2 x^3 \sqrt {x^4+9} dx$ Let us consider $a =x^4+9 \implies da=4x^3 dx$ Now, $ \dfrac{2 \pi}{27} \int_0^2 \dfrac{\sqrt a da}{4}= \dfrac{\pi}{54}[ (2/3) a^{3/2} ]_0^2$ Thus, $Surface \space Area=\dfrac{98 \pi}{81}$
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