f=e^y-xy-e
dy/dx=-(df/dx)/(df/dy)=-(e^y-x)/(-y)=(e^y-x)/y
x=0 ∴y=1
dy/dx=(e-0)/1=e
切线方程：y-1=ex y=ex+1
法线方程：y-1=-1/e*x y=x/e +1