1)(a^2-b^2)+(-a+b)=(a-b)(a+b)-(a-b)=(a-b)(a+b-1)
2)(x^3-x^2y)+(-xy^2+y^3)=x^2(x-y)-y^2(x-y)=(x-y)(x^2-y^2)=(x-y)(x-y)(x+y)=(x-y)^2(x+y)
3)(a^3+a^2b)+(-ab^2-b^3)=a^2(a+b)-b^2(a+b)=(a+b)(a^2-b^2)=(a+b)(a-b)(a+b)=(a-b)(a+b)^2
4)(m^2+2mn+n^2)+(-mb -nb)=(m+n)^2-b(m+n)=(m+n)(m+n-b)