∂z/∂x=e^(x²+y²)*(x²+y²)'=2xe^(x²+y²)∂z/∂y=e^(x²+y²)*(x²+y²)'=2ye^(x²+y²)所以dz=2xe^(x²+y²)dx+2ye^(x²+y²)dy
z=e^(x2+y2)dz=2xe^(x2+y2)dx+2ye^(x2+y2)dy
dz = e^(x²+y²)d(x²+y²) = e^(x²+y²)(2xdx+2ydy) =2e^(x²+y²)(xdx+ydy)