若i(x+yi)=3+4i,x,y∈R,则复数x+yi的模是(  ) A.2 B.3 C.4 D.

若i(x+yi)=3+4i,x,y∈R,则复数x+yi的模是(  ) A.2 B.3 C.4 D.5
2025-06-23 00:38:21
推荐回答(1个)
回答1:

∵i(x+yi)=xi-y=3+4i,x,y∈R,∴x=4,-y=3,即x=4,y=-3.
∴|x+yi|=|4-3i|=
4 2 +(-3 ) 2
=5.
故选D.