V=π∫[0,1](arcsin(y))^2 dy　：x=arcsin(y)、y=sin(x)→dx=dy/√(1-y^2)=dy/cos(x)
=π∫[0,π/2] x^2･cos(x) dx
=π{x^2･sin(x)-2∫x･sin(x)dx}_[0,π/2]
=π^3/4-2π{-x･cos(x)+∫cos(x)dx}
=π^3/4-2π(sin(x))_[0,π/2]
=π^3/4-2π