xy-e^y=0y+xdy/dx-e^y·dy/dx=0dy/dx=y/(e^y-x)d²y/dx²=[dy/dx·(e^y-x)-y(e^y·dy/dx-1)]/(e^y-x)²把dy/dx=y/(e^y-x)代入上式得d²y/dx²=[y-y²e^y/(e^y-x)]/(e^y-x)²