Z1/z2=(3+i)/(1-2i)=(3+i)(1+2i)/[(1-2i)(1+2i)]=
=(3+6i+i-2)/(1+4)=(1+7i)/5=0,2+1,2i
((a²-16b²)/(4ab))/(1/(4b)-1/a)=((a²-16b²)/((4ab))/(a-4b)/(4ab))=
=(a-4b)(a+4b)(4ab)/((a-4b)(4ab))=a+4b=40/13+4*(55/13)=
=40/13+220/13=260/13=20.
7х-(5х-(3х+у)=7х-5х+(3х+у)=7х-5х+3х+у=5х+у