Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 5 - Applications of Integration - Review - Exercises - Page 393: 9

Answer

$\frac{1656}{5} \pi$

Work Step by Step

Given $$ x=0, \quad x=9-y^2 ; \quad \text { about } x=-1$$ find the intersection points \begin{aligned} 9-y^2&=0\\ (3-y)(3+y)&=0 \end{aligned} then $$y=-3,\ \ \ y=3$$ To find the volume of the solid when the bounded region rotate about $ x=-1$. \begin{aligned} V&= \pi\int_a^b[R^2(y)- r^2(y)]dy \end{aligned} Here $$R= 9-y^2+1= 10-y^2,\ \ \ r= 1 $$ Hence \begin{aligned} V&=\pi \int_a^b[R^2(y)- r^2(y)]dy \\ & =2 \pi \int_0^3\left[\left(10-y^2\right)^2-1\right] d y\\ &=2 \pi \int_0^3\left(100-20 y^2+y^4-1\right) d y \\ & =2 \pi \int_0^3\left(99-20 y^2+y^4\right) d y\\ &=2 \pi\left[99 y-\frac{20}{3} y^3+\frac{1}{5} y^5\right]_0^3 \\ & =2 \pi\left(297-180+\frac{243}{5}\right)\\ &=\frac{1656}{5} \pi \end{aligned}
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