f'x=3x^2-3y f'y=3y^2-3x f'x=0,f'y=0 即x^2-y=0 y^2-x=0 消去y x^4-x=0 即x(x-1)(x^2+x+1)=0 x=0或1 y=0或1 x=y=0时f(x,y)=0 x=y=1时f(x,y)=-1
