1.先对x积分,积分区域为：0《y《1,0《x《y
∫∫e^(-y^2)dxdy=∫(0,1)e^(-y^2)dy∫(0,y)dx
=∫(0,1)ye^(-y^2)dy=(-1/2)e^(-y^2)|(0,1)=(1-1/e)
2.用柱面坐标：积分区域为 r《2sinθ,0《θ《π
∫∫(x^2+y^2)dxdy=∫(0,π)dθ∫(0,2sinθ)r^3dr
=4∫(0,π)(sinθ)^4dθ=8∫(0,π/2)(sinθ)^4dθ=8*(3/4)(1/2)(π/2)=3π/2
3.分D为两部分,D1：^2+y^2《4,D2：