How to find Uab and Ucd in this circuit

[dado]

Homework Statement

How to find Uab and Ucd in this circuit
http://img830.imageshack.us/img830/2852/556d.png

Homework Equations

The Attempt at a Solution

I have no idea how to find it.
I think that Uab=R*I

 

[zorro]

To find Uab you have to find the potential drop across the resistor R1.
Try to simplify the circuit.
Hint : R3 and R5 are in parallel connection.

 

[dado]

thank you.
can you explain me what that wire marked in red means?

[PLAIN]http://img822.imageshack.us/img822/2316/lkkj.png

 

[zorro]

What do you think it means?

 

[gneill]

Homework Statement

How to find Uab and Ucd in this circuit
http://img830.imageshack.us/img830/2852/556d.png

Homework Equations

The Attempt at a Solution

I have no idea how to find it.
I think that Uab=R*I

I don't see any voltage or current sources in that circuit, so if "Uab means R*I" then I suppose _you_ mean that it's the equivalent resistance "seen" between nodes a and b. Right?