About complex number
2009-09-13 3:54 am
If the expression (a + 3i) (-2 + 3i) is a real number, find the value of the real number a.
回答 (1)
2009-09-13 4:02 am
✔ 最佳答案
(a + 3i) (-2 + 3i)=-2a+3ai-6i-9
=(-2a-9)+(3a-6)i
Since it is a real number, 3a-6=0=>a=2
The value is 2(-2)-9=-13
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