首页 > 留学知识库

问题: 求实数

设a是实数,且a/(1+i)+(1+i)/2是实数,则a=( )
A.1/2
B.1
C.3/2
D.2
请写出过程

解答:

设a是实数,且a/(1+i)+(1+i)/2是实数,则a=( )
[a/(1+i)]+(1+i)/2
=[a(1-i)/(1+i)(1-i)]+[(1+i)/2]
=[a(1-i)/(1×1-i×i)][(1-i)/2]
={a(1-i)/[1-(-1)]+[(1-i)/2] i×i=-1
=[a×(1-i)/2]+(1/2)+(i/2)
=(a/2)-(ai/2)+(1/2)+(i/2)
∵a/(1+i)+(1+i)/2是实数,a是实数
∴ai/2=i/2 a=1