Thevenin equivalent with multiple sources circuit
Finally I've got something of interesting. I was told to use the Thevenin theorem between points C and D instead. C is located on the middle node and D under the 10 ohms resistance.
I've summed up everything on that picture, the Rth is 0 ohm because the the circuited voltage source gives a wire with 0 ohms along it, and it is in parallel with the two other resistance, right?
And for Eth, I knew the voltage between two branches is supposed to be the same, thats why Eth equals 20 volts.
Thanks you Phil!