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`
