b) Tính A + B; A – B.

b) Ta có:

• A + B = (4x6 – 2x2y3 – 5xy + 2) + (3x2y3 + 5xy – 7)

= 4x6 – 2x2y3 – 5xy + 2 + 3x2y3 + 5xy – 7

= 4x6 + (3x2y3 – 2x2y3) + (5xy – 5xy) + (2 – 7)

= 4x6 + x2y3 – 5.

• A – B = (4x6 – 2x2y3 – 5xy + 2) – (3x2y3 + 5xy – 7)

= 4x6 – 2x2y3 – 5xy + 2 – 3x2y3 – 5xy + 7

= 4x6 – (3x2y3 + 2x2y3) – (5xy + 5xy) + (2 + 7)

= 4x6 – 5x2y3 – 10xy + 9.

Vậy A + B = 4x6 + x2y3 – 5; A – B = 4x6 – 5x2y3 – 10xy + 9.