e^(x+y)+xy=0求一阶导数和二阶导数

e^(x+y)+xy=0两边对x求导得：
e^(x+y)*(1+y')+y+xy'=0,解得：y'=-(e^(x+y)+y)/((e^(x+y)+x))=(xy-y)/(x-xy)
e^(x+y)*(1+y')+y+xy'=0两边对x求导得：
e^(x+y)*(1+y')^2+y''e^(x+y)+2y'+xy''=0
解得：y''=-(e^(x+y)*(1+y')^2+2y')/((e^(x+y)+x))
=(xy(1+y')^2-2y')/(x-xy) 代入y'=(xy-y)/(x-xy)即可