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问题: 初二数学

(a方-a-2)(a方+2a-3)
--------------------
(a-2)(a-1)(a+1)
如何得
(a+1)(a-2)(a+3)(a-1)
--------------------
(a-2)(a-1)(a+1)
结果?
请把每步的过程说的细些,谢谢!

解答:

(a方-a-2)(a方+2a-3)
--------------------
(a-2)(a-1)(a+1)
ax^+bx+c=0的两个根为x1,x2
则ax^+bx+c=a(x-x1)(x-x2)成立
a^-a-2=0的两个根为2,-1 a^-a-2=(a+1)(a-2)
a^+2a-3=0的两个根为-3,1 a^+2a-3=(a-1)(a+3)
(a方-a-2)(a方+2a-3)
--------------------
(a-2)(a-1)(a+1)

(a+1)(a-2)(a+3)(a-1)
=--------------------
(a-2)(a-1)(a+1)
==a+3
Are you understand?