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问题
选择题
复数
1
1+i
的虚部为( )
A.-l
B.-i
C.-
1
2
D.
-
1
2
i
答案
1
1+i
=
(1-i)
(1+i)(1-i)
=
1-i
2
=
1
2
-
i
2
.
所以,复数
1
1+i
的虚部为
-
1
2
.
故选C.
解答题
若一个数的平方根是3a+2和2a-1,求这个数.
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选择题
— What's that terrible noise? It's noisy.
— The neighbors ____ for a party.
A. have prepared
B. are preparing
C. prepare
D. will prepare
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