x(x-2y)=y(2y-x)
x(x-2y)+y(x-2y)=0
(x+y)(x-2y)=0
x=-y,或x=2y

当x=-y时,(x²-y²)/xy = 0
当x=2y时,(x²-y²)/xy = ,(4y²-y²)/(2y²) = 3/2