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2. (5 分) 复数 $\frac{5 i}{1-2 i}=(\quad)$

Gaokao · Math · previous-year question

  1. A.$2-\mathrm{i}$
  2. B.$1-2 \mathrm{i}$
  3. C.$-2+i$correct
  4. D.$-1+2 i$

Answer

C. $-2+i$

Explanation

解: $\frac{5 i}{1-2 i}=\frac{5 i(1+2 i)}{(1-2 i)(1+2 i)}=-2+i$ 故选: C.

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