F(x,y,z)=arctan(y/x)-z∂F/∂x=-y/(x²+y²)∂F/∂y=x/(x²+y²)∂F/∂z=-1曲面在M0点的法向量是(∂F/∂x,∂F/∂y,∂F/∂z) | M0 =(...