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