Làm tính nhân: (xy – 1)(xy + 5).
Giải thích
(xy – 1)(xy + 5)
= xy.(xy + 5) + (–1).(xy + 5)
= xy.xy + xy.5 + (–1).xy + (–1).5
= x2y2 + 5xy – xy – 5
= x2y2+ 4xy – 5.
(xy – 1)(xy + 5)
= xy.(xy + 5) + (–1).(xy + 5)
= xy.xy + xy.5 + (–1).xy + (–1).5
= x2y2 + 5xy – xy – 5
= x2y2+ 4xy – 5.