Câu 6:
c.
1. $x^{2} - x - 6$
$= x^{2} + 2x - 3x - 6$
$= x(x + 2) - 3(x + 2)$
$= (x + 2)(x - 3)$
2. $x^{3} - x^{2} - 14x + 24$
$= x^{3} - 2x^{2} + x^{2} - 2x - 12x + 24$
$= x^{2}(x - 2) + x(x - 2) - 12(x - 2)$
$= (x - 2)(x^{2} + x - 12)$
$= (x - 2)(x^{2} + 4x - 3x - 12)$
$= (x - 2)\left [ x(x + 4) - 3(x + 4) \right ]$
$= (x - 2)(x + 4)(x - 3)$
3. $x^{3} + 8x^{2} + 19x + 12$
$= x^{3} + x^{2} + 7x^{2} + 7x + 12x + 12$
$= x^{2}(x + 1) + 7x(x + 1) + 12(x + 1)$
$= (x + 1)(x^{2} + 7x + 12)$
$= (x + 1)(x^{2} + 4x + 3x + 12)$
$= (x + 1)\left [ x(x + 4) + 3(x + 4) \right ]$
$= (x + 1)(x + 4)(x + 3)$
4. $x^{3} + 6x^{2} + 11x + 6$
$= x^{3} + x^{2} + 5x^{2} + 5x + 6x + 6$
$= x^{2}(x + 1) + 5x(x + 1) + 6(x + 1)$
$= (x + 1)(x^{2} + 5x + 6)$
$= (x + 1)(x^{2} + 3x + 2x + 6)$
$= (x + 1)\left [ x(x + 3) + 2(x + 3) \right ]$
$= (x + 1)(x + 3)(x + 2)$
