z=a+bi
a,b∈R
(1+2i)(a+bi)+4-i=6+2i
a+2ai+bi-2b+4-i-6-2i=0
(a-2b-2)+(2a+b-3)i=0
所以a-2b-2=0
2a+b-3=0
a=8/5,b=-1/5
z=8/5-i/5