Answer to Question #258929 in Calculus for Lie

Question #258929

R is the region bounded by x = y


2 + 1 and x = 9 − y


2


and the axis


of revolution is x = 9.

1
Expert's answer
2021-11-01T18:45:38-0400




y2+1=9y2y^2+1=9-y^2

2y2=82y^2=8

y2=4y^2=4

y1=2,y2=2y_1=-2, y_2=2

A(x)=π(outer radius)2π(inner radius)2A(x)=\pi(outer\ radius)^2-\pi (inner\ radius)^2

=π(9(y2+1))2π(9(9y2))2=\pi (9-(y^2+1))^2-\pi(9-(9-y^2))^2

=π(8118y218+y4+2y2+1=\pi(81-18y^2-18+y^4+2y^2+1

81+16218y281+18y2y4)-81+162-18y^2-81+18y^2-y^4)

=π(16y2+64)=\pi(-16y^2+64)


V=22π(16y2+64)dy=32π02π(y2+4)dV=\displaystyle\int_{-2}^2\pi(-16y^2+64)dy=32\pi\displaystyle\int_{0}^2\pi(-y^2+4)d

=32π[y33+4y]20=32π(833+8)=32\pi\bigg[-\dfrac{y^3}{3}+4y\bigg]\begin{matrix} 2 \\ 0 \end{matrix}=32\pi(-\dfrac{8^3}{3}+8)

=512π3(units3)=\dfrac{512\pi}{3} (units^3)


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