d) (x – y)(x^2 – xy – y^2).
Giải thích
d) (x – y)(x2 – xy – y2)
= x.x2 + x.(‒xy) + x.(‒y2) + (‒y).x2 + (‒y).(‒xy) + (‒y).(‒y2)
= x3 ‒ x2y ‒ xy2 ‒ x2y + xy2 + y3
= x3 + (‒ x2y ‒ x2y) +(‒ xy2 + xy2) + y3
= x3 ‒ 2x2y + y3.
d) (x – y)(x2 – xy – y2)
= x.x2 + x.(‒xy) + x.(‒y2) + (‒y).x2 + (‒y).(‒xy) + (‒y).(‒y2)
= x3 ‒ x2y ‒ xy2 ‒ x2y + xy2 + y3
= x3 + (‒ x2y ‒ x2y) +(‒ xy2 + xy2) + y3
= x3 ‒ 2x2y + y3.