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# 一題 克拉馬公式(3) 請速來

已知二直線L1：(a-1)x-(a-2)y=1，L2：9x+(a-2)(a+5)y=5平行(a屬於實數)，則a=？

Update:

a不只一個答案。

請再多想想。

### 1 Answer

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- 1 decade agoFavorite Answer
若兩直線

L1: bx+cy=d

L2: ex+fy=g

則兩線平行即

b/e=c/f

answer

(a-1)/9=-(a-2)/[(a-2)(a+5)]

a^2+4a+4=0

a=-2

2008-11-25 07:55:34 補充：

還有一個trivial solution

a=2 帶入原式

L1: x=1

L2: x=5/9

故另一解為 a=2

Source(s): me

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