使用直角坐标,∫∫(x^2-y^2)dxdy =∫[0,π]dx∫[0,sinx](x^2-y^2)dy =∫[0,π](x^2y-1/3y^3)|[0,sinx]dx=∫[0,π](x^2sinx-1/3(sinx)^3)dx=∫(x^2sinx-1/3(sinx)^3)dx=-x^2cosx+2xsinx+2cosx-∫1/3(sinx)^3dx=-x^2co...