df/dx=3x^2-3y=0df/dy=3y^2-3x=0得驻点(0,0) (1,1) A=d^2f/dx^2=6xC=d^2f/dy^2=6yB=d^2f/dxdy=-3①对驻点(0,0) A=0 B=-3 C=0因为B^2-AC>0,所以f(0,0)不是极值点②对驻点(1,1)A=6 B=-3 C=6因为B^2-AC0,所以f(1,1)是极...