逍遙人 asked in 科學數學 · 1 decade ago

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 ago
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    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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