应为∑的母线与z轴平行，所以∫∫(∑) y^2*zdxdy=0原式=∫∫(∑) xdydz=∫∫(Dyoz) √(1-y^2)dydz=∫(0,1)dz*∫(0,1)√(1-y^2)dy=1*[(1/2)*arcsiny+(y/2)*√(1-y^2)]|(0,1)=π/4
