x2+2xy+y2+3x+3y−18 x2+2xy+3x+y2+3y−18 x2+2xy−3x+6x+y2−3y+6y−18 x2+2xy−3x+y2−3y+6x+6y−18 x2+xy−3x+xy+y2−3y+6x+6y−18 x(x + y - 3) + y(x + y - 3) + 6(x + y - 3) = (x + y - 3)(x + y + 6) = (x + y + 6)(x + y -3)