U1=12+7I;
Abs[U1]

Arg[U1]

U2m=15;
fi=(π/3);
U2=U2m*(E^(I*fi))

%//N

(*priklad 3*)

U3=9.2*(E^(I*2.4))

U4=12.8+5.2I;
ω=200;
Plot[Im[U4*(E^(I*ω*t))], {t, 0, 0.1}]