Làm tính nhân: a) (x^2 – xy + 1)(xy + 3).
Giải thích
a) (x2 – xy + 1)(xy + 3)
= x2 . xy – xy . xy + 1 . xy + x2 . 3 – xy . 3 + 1 . 3
= x3y – x2y2 + xy + 3x2 – 3xy + 3
= x3y – x2y2 + (xy – 3xy) + 3x2 + 3
= x3y – x2y2 – 2xy + 3x2 + 3.
a) (x2 – xy + 1)(xy + 3)
= x2 . xy – xy . xy + 1 . xy + x2 . 3 – xy . 3 + 1 . 3
= x3y – x2y2 + xy + 3x2 – 3xy + 3
= x3y – x2y2 + (xy – 3xy) + 3x2 + 3
= x3y – x2y2 – 2xy + 3x2 + 3.