4x方-8xy+4y方/2x方-2y方
=(4x^2-8xy+4y^2)/(2x^2-2y^2)
=[4(x^2-2xy+y^2)]/[2(x^2-y^2)]
=4(x-y)^2/2(x+y)(x-y)
=2(x-y)/(x+y)