x^5+x^4y-2x^3y^2-x^2y^3-xy^4+2y^5
=x^3(x^2+xy-2y^2)-y^3(x^2+xy-2y^2)
=(x^2+xy-2y^2)(x^3-y^3)
=(x+2y)(x-y)(x-y)(x^2+xy+y^2)
=(x+2y)(x-y)^2(x^2+xy+y^2)