(*Tyden 8, cv 4*)
ClearAll["Global`*"]
rovnice={
0==IU+IR1+IC1,
IR1+IC1==IR2,
IR2==IL1,
U1-U2==IR1*R1,
U1-U2==IC1*(1/(I*ω*C1)),
U2-U3==IR2*R2,
U3==IL1*I*ω*L1,
U==U1
};
soucastky={R1->(10^4),R2->(10^4), C1->(10^(-8)),L1->(10^(-2)),U->4.2+3.1I};
omega={ω->2π*1000};
reseni=Solve[rovnice/.soucastky, {U1,U2,U3,IU,IR1,IR2,IL1,IC1}];
Plot[Im[U2*(E^(I*ω*t))/.reseni/.omega], {t, 0, 0.005}]
LogLogPlot[Abs[(U2/U1)/.reseni], {ω,10,(10^7)}, PlotRange->All]

R1=R2=(10^4);
C1=(10^(-8));
L1=(10^(-2));
U=4.2+3.1I;
ZR1=R1;
ZR2=R2;
ZC1=(1/(I*ω*C1));
ZL1=I*ω*L1;
Z1=(1/((1/ZR1)+(1/ZC1)));
Z2=ZR1+ZL1;
Zin=Z1+Z2;
Zout=Z2;
Uout=U*(Zout/Zin);
Plot[Im[Uout*(E^(I*ω*t))/.{ω->2π*1000}], {t, 0, 0.005}]
LogLogPlot[Abs[(Uout/U)], {ω,10,(10^7)}, PlotRange->All]
LogLogPlot[Abs[Zin], {ω,10,(10^7)}, PlotRange->All]