题目若是求：z=x^2+2y^2及 z=6-2x^2-y^2 所围成的立体的体积,则为
D: x^2+y^2=2
V=∫∫[(6-2x^2-y^2)-(x^2+2y^2)]dxdy=3∫∫(2-x^2-y^2)dxdy
=3∫dθ∫