1 e^z=xyz
e^zz'x=yz+xyz'x z'x=yz/(xy-e^z)=yz/(xy-xyz)=z/(x-xz)
类似 z'y=z/(y-yz)
dz=[z/(x-xz)]dx+[z/(y-yz)]dy
2.立体在xoy坐标面的投影D：x^2+y^2《2
V=∫∫(2-x^2-y^2)dxdy,用极坐标
=∫(0,2π)dθ∫(0,√2)r(2-r^2)dr
=2π(2-1)
=2π