f.2 factorization

1.
x2 + 3x - 4
= x2 - x + 4x - 4
= (x2 - x) + (4x - 4)
= x(x - 1) + 4(x - 1)
= (x + 4)(x - 1)


2.
x2 - 6x + 5
= x2 - 5x - x + 5
= (x2 - 5x) + (-x + 5)
= x(x - 5) - 1(x - 5)
= (x - 1)(x - 5)


3.
2a2b2 - 4ab
= 2(ab)(ab) - 2(2)(ab)
= 2(ab)[(ab) - 2]
= 2ab(ab - 2)


4.
3ab - 6
= 3(ab) - 3(2)
= 3[(ab) - (2)]
= 3(ab - 2)


5.
2a2b2 - ab - 6
= 2a2b2 + 3ab - 4ab - 6
= [2(ab)2 + 3(ab)] + [-2(2)(ab) - 2(3)]
= (ab)[2(ab) + 3] - 2[(2)(ab) + (3)]
= ab(2ab + 3) - 2(2ab + 3)
= (ab - 2)(2ab + 3)

2009-10-07 00:01:35 補充：
沒有辦法啦，用 cross method 所列的 steps 等於沒有 step。
其實我用的方法就是 cross method 的來源。

The solution of 老爺子 is too complicated.
Just simply use the method of cross method to find out the answer.