5x^2-10xy+5y^2-2x+2y
=(5x^2-10xy+5y^2)－(2x－2y)
=5(x²－2xy＋y²)－2(x－y)
=5(x－y)²－2(x－y)
=(x－y)[5(x－y)－2]
=(x－y)(5x－5y－2)