Question

已知i是虚数单位，则

1-2i

2+i

等于______．

Answer 1

1-2i

2+i

=

(1-2i)(2-i)

(2+i)(2-i)

=

2+2i2-i-4i

( 22+12 )2

=

-5i

5

=-i．
故答案为-i．