>>951
V=πa^3∫[0,2π](1−cos(θ))^3dθ
 =πa^3∫[0,2π](1−3cos(θ)+3cos^2(θ)−cos^3(θ))dθ
 =πa^3∫[0,2π](1−3cos(θ)+(3cos(2θ)+1)/2−(3cos(θ)+cos(3θ))/4)dθ
 =πa^3[(θ−3sin(θ)+3(sin(2θ)+x)/2−3(sin(θ)+sin(3θ))/4)][0,2π]
 =(7/2)π^2*a^3