z=arctan(x+y)/(1-xy)的全微分。

z对x的偏导数：[1/(x+y)²(1-xy) + yarctan(x+y)]/(1-xy)² =[1 + y(x+y)²(1-xy)arctan(x+y)]/[(1-xy)³(x+y)²] z对y的偏导数：[1/(x+y)²(1-xy) + xarctan(x+y)]/(1-xy)² =[1 + x(x+y)²(1-xy)arctan(x+y)]/[(1-xy)³