因式分解的問題

1)
a^2-9b^2
=(a+3b)(a-3b)

2)
1分之3b^2-12
=3b^2-12
=3(b^2-4)
=3(b+2)(b-2)

3)
2x^3-16
=2(x^3-8)
=2(x-2)(x^2+2x+4)

4)
6x^2-11xy-10y^2
=(2x-5)(3x+2)

5)
x^2+8x+12
=(x+6)(x+2)

6)
6x^2+7x-20
=(3x-4)(2x+5)

7)
(a^2-a-72)+(ab+8b)
=(a-9)(a+8)+b(a+8)
=(a+8)(a+b-9)

2008-08-05 12:10:14 補充：
我係絕對冇抄上面果位，只係我回答中ge時候，佢已經遞交了。

1, a^2-9b^2
= a^2-(3b)^2
= (a- 3b)(a+3b)

2, 1分之3b^2-12
= 1/3b^2-12
=b^2-4
=b^2-2^2
=(b-2)(b+2)

3, 2x^3-16
=(2) (x^3-8)
=(2) (x^3-2^3)
=(2) (x-2)(x^2+4x-4)

4, 6x^2-11xy-10y^2
=(2x-5y)(3x+2y)

5, x^2+8x+12
=(x+2)(x+6)

6, 6x^2+7x-20
=(2x+5)(3x-4)

7, (a^2-a-72)+(ab+8b)
=(a+8)(a-9) + b(a+8)
=(a+8)(a-9+b)