一條中四數唔識計

2010-09-15 1:54 am

條數就係:

If the expression (a+3i)(-2+3i) is a real number,find the value of
the real number a

係一條complex number既數

麻煩幫幫手..唔識計

我要埋詳細既解答 thz

更新1:

補充一下答案係a=2 求步驟

更新2:

答案係 -2 先岩答案係 -2 先岩答案係 -2 先岩

更新3:

- -..sorry 我記錯答案下面答果個係岩架..sorsor a=2

回答 (1)

2010-09-15 2:32 am

✔ 最佳答案

(a+3i)(-2+3i)
=-2a+3ai-6i+9i^2
=-2a+(3a-6)i-9
=-(2a+9)+(3a-6)i

Since (a+3i)(-2+3i) is real, the imaginary part=0
i.e. 3a-6=0 => a=2

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