企源知识库

求函数的全微分：
z=xe^-xyy+sin(xy)
【正确答案】：dz=e^-xydx+xe^-xy(-ydx-xdy)+cos(xy)(ydx+xdy) =[e^-xyxye^-xy+ycos(xy)]dx+[-x²e^-xy+xcos(xy)]dy．