2x^2-6xy+9y^2-4x+4=0
x^2-6xy+9y^2+x^2-4x+4=0
(x-3y)^2+(x-2)^2=0
x-3y=0
x-2=0
x=2,y=2/3
则y/x-x/y=1/3-3=-8/3