I=,-I 2 [J(x2+y2)dxdydz-[(x2+y2)dxdydz, 2 8 r·r2=π, 3 25 D 2 ndz 6 原式I 4525 π=336兀, 36 上页( ) ( ) , 1 2 2 2 2 2 1 2     = + − +  = − x y dxdydz x y dxdydz I I I   =  1 2 8 2 1 D I rdrd r fdz , 3 4 5 =    =  2 2 2 2 2 D I rdrd r fdz , 6 2 5 =  原式I =  3 4 5 −  6 2 5 = 336 .    =    8 2 4 0 2 0 2 2 r d dr r r dz    =    2 2 2 0 2 0 2 2 r d dr r r dz