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V=4Ïâ«(1,3)xydx=4Ïâ«(1,3)xâ[1-(x-2)^2dx
=-2Ïâ«(1,3)[(x-2)+2]â[1-(x-2)^2]d[1-(x-2)^2]
=-2Ï(2/3)â[1-(x-2)^2]^3](1,3)+8Ïâ«(1,3)â[1-(x-2)^2d(x-2)
=0+4Ï{(x-2)â[1-(x-2)^2]+arcsin(x-2)}(1,3)
=4Ï[0+arcsin1-arcsin(-1)]=4Ï[Ï/2-(-Ï/2)]=4Ï^2
不懂求具体点