Ig1=j2mA

Ig3=jmA

Ig4=0.5mA

E2=1V

R2=2kΩ

R5=1kΩ

R6=4kΩ

C=2μF

ω=10^4 s^-1

and i have to find complex value of voltage U shown in the picture

When doing examples like this, the easiest way for me is to use Thevenin's theorem, and it could work just fine if i had to find Thevenin impedance, because, when finding Thevenin impedance, every voltage generator is short circuit and every branch with current generator can be removed, so i have that Thevenin impedance is R2, but i don't know how to find Thevenin generator since i have a few unknown values in the circuit.