f(x,y)=e^xy x y=2
求全微分 (Df/Dx)dx (Df/Dy)dy=0
dy/dx=-(y*e^xy 1)/(x*e^xy 1)
如果 x=1
dy/dx |x=1 = -(ye^y 1)/(e^y 1)
其中y为 f(1,y)=2 的解,即y满足 e^y 1 y=2=