两边对x求导,把y看成是x的复合函数：
lny+xy'/y+y'e^(xy)+ye^(xy)(y+xy')=0
y'[x/y+e^(xy)+xye^(xy)]=-lny-y²e^(xy)
得y'=-[lny+y²e^(xy)]/[x/y+e^(xy)+xye^(xy)]