Ta có
$x^3+x^2y-3x^2-5xy-y^2-4x-y = (x^3 + x^2y + x^2) -(4x^2 + 4xy + 4x) -(xy + y^2 + y)$
$= x^2(x + y + 1) - 4x(x + y + 1) - y(x + y + 1)$
$= (x^2 - 4x - y)(x + y + 1)$
Lại có
$x^3-2x^2y-x^2+xy-2y^2+x-3y-1 = (x^3- 2x^2y - x^2) + (xy - 2y^2 - y) + (x - 2y - 1)$
$= x^2(x - 2y - 1) + y(x-2y-1) + (x-2y-1)$
$= (x^2 + y + 1)(x - 2y - 1)$