z=ln(x^2+y^2)先求x,y的偏导,再求全微分δz/δx=2x/(x^2+y^2)δz/δy=2y/(x^2+y^2)所以dz=(δz/δx)*dx+(δz/δy)*dy=2xdx/(x^2+y^2)+2ydy/(x^2+y^2)=(2xdx+2ydy)/(x^2+y^2)如果不懂,请Hi我,祝学习愉快!...