Question

difficult exercise circuits. (attachment) u can give me answer,wenn Im offline, too.

Answer 1

For this problem, you need to use
Ohm's law : V=IR (V=voltage, I=current, R=resistance, in consistent units)
and
Kirchhoff's law: \(\sum currents~ at~ a~ node = 0\)
Start by enumerating the currents at each node, using as much as possible the variables i0, i1 and RL, which will be the independent variables of the function UL (voltage across the constant current source).

To review Kirchhoff's law, see for example:
https://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.KCL.html