Đáp án:
a) $-xy (x^{2} + xy - y^{2})$
$= -x^{3}y - x^{2}y^{2} + xy^{3}$
b) $(x^{2} - 2x - 1)(x - 3)$
$= x^{3} - 2x^{2} - x - 3x^{2} + 6x + 3$
$= x^{3} + (-2x^{2} - 3x^{2}) + (-x + 6x) + 3$
$= x^{3} + (-5x^{2}) + 5x + 3$
$= x^{3} - 5x^{2} + 5x + 3$
$c) (x + 2)^{3} - x^{2}(x + 6) - 10$
$= x^{3} + 3x^{2}2 + 3x2^{2} + 2^{3} - (x^{3} + 6x^{2}) - 10$
$= x^{3} + 6x^{2} + 12x + 8 - x^{3} - 6x^{2}) - 10$
$= (x^{3} - x^{3}) + (6x^{2} - 6x^{2}) + 12x + (8 - 10)$
$= 0 + 0 + 12x + (-2)$
$= 0 + 0 + 12x - 2$
d) $(x - 2)^{3} - x^{2}(x - 6) - 2(6x + 7)$
$= x^{3} - 3x^{2}2 + 3x2^{2} - 2^{3} - (x^{3} - 6x^{2}) - (12x + 14)$
$= x^{3} - 6x^{2} + 12x - 8 - x^{3} + 6x^{2} - 12x - 14$
$= (x^{3} - x^{3}) + (-6x^{2} + 6x^{2}) + (12x - 12x) + (-8 - 14)$
$= 0 + 0 + 0 + (-22)$
$= - 22$
