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: 8

Answer

$ \frac{284\pi }{15}$

Work Step by Step

Given $$ x=1+y^2\ \ \ \ y= x-3\ \ \ \text{about } y-axis$$ First , we find the intersection points \begin{aligned} 1+y^2&= y+3\\ y^2-y-2&=0\\ (y+1)(y-2)&=0 \end{aligned} Then $$y= -1,\ \ \ y=2 $$ Since $$y+3\geq 1+y^2,\ \ \ \ -1\leq y\leq 2 $$ Then the outer radius $R= y+3$ and the inner $r=1+y^2$ Hence , by using washer method, we have \begin{aligned} V &=\pi\int_a^b[R^2-r^2]dy\\ & =\pi \int_0^2\left[(y+3)^2-\left(1+y^2\right)^2\right] dy\\ &= \pi \int_0^2 [-y^4-y^2+6y+8]dy\\ &= \pi \left(-\frac{1}{5}y^5-\frac{1}{3}y^2+3y^2+8y\right)\bigg|_0^2\\ &= \frac{284\pi }{15} \end{aligned}
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