giúp mik bài 3 vs maayys bạn eiiiii

a.

`A = a(b + 3) – b(3 + b)`

`=a(b + 3) – b(b + 3)`

`=(b + 3)(a – b)` (1)

Thay a = 2003, b = 1997 vào (1), ta có:

`=(1997 + 3)(2003 – 1997)`

`=2000 * 6 = 12000`

b.

`B = b^2 – 8b – c(8 – b)`

`=(b^2 – 8b) – c(8 – b)`

`=b(b – 8) – c(8 – b)`

`=-b(8 – b) – c(8 – b)`

`=-(8 – b)(b + c)` (2)

Thay b = 108, c = -8 vào (2), ta có:

`=-(8-108)[108 + (-8)]`

`=10000`

c.

`C = xy(x + y) – 2x – 2y`

`=xy(x + y) – (2x + 2y)`

`=xy(x + y) – 2(x + y)`

`=(x + y)(xy – 2)` (3)

Thay xy = 8, x + y = 7 vào (3), ta có:

`=7 * (8 – 2)`

`=42`

d.

`D = x^5(x + 2y) – x^3y(x + 2y) + x^2y^2(x + 2y)`

`=(x + 2y)(x^5 – x^3y + x^2y^2)` (4)

Thay x = 10, y = -5 vào (4), ta có:

`=[10 + 2 * (-5)][10^5 – 10^3*(-5) + 10^2*(-5)^2]`

`=0`