x^2+4y^2-4x+4y+5=0(x-2)^2+(2y+1)^2=0所以有x-2=0 2y+1=0所以x=2 y=-1/2[（x^4-y^4)/xy]*[(2x^2-xy)/(xy-y^2)]/{(x^2+y^2)/y}^2.=[(4-1/4)/1]*[(8-1)/(1-1/4)]/[(4+1/4)/1/4]^2=35/289
