xdy-ydx=y²e^ydyxy'-y=y²e^y(xy'-y)/y²=e^y凑微分，因为(x/y)'=(y-xy')/y²所以(x/y)'=-e^y两边同时积分得(x/y)=-e^y+Cx=-ye^y+Cyx=y(C-e^y)
