Calculus 8th Edition

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

Chapter 5 - Applications of Integration - 5.3 Volumes by Cylindrical Shells - 5.3 Exercises - Page 382: 31

Answer

The region bounded by $x= 0 ,\ \ x=\frac{1}{y^2} ,\ \ y=1,\ \ y=4 $ rotates about $y=-2$

Work Step by Step

Given $$ 2 \pi \int_1^4 \frac{y+2}{y^2} d y $$ Rewrite the integral as the following $$ 2 \pi \int_1^4 (y+2)\left(\frac{1}{y^2}\right) d y $$ Compare with $$V= \int_a^b 2\pi r(y) h(y)dy$$ Here $r(y)= y+2,\ \ h(y)=\frac{1}{y^2}$. This represents the volume of the generated solid when the region bounded by $$x= 0 ,\ \ x=\frac{1}{y^2} ,\ \ y=1,\ \ y=4 $$ rotate about $y=-2$
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