I am not understanding how Rth is calculated.. What I've been doing is visualizing the path that the current would make. Rth is then the equivalent resistance of those resistors that current travels through. Is that how it's suppose to be done? Anyways... if you look at my pictures... the current can take the paths: Left picture: Current does not travel through branch containing R2 or R2k due to short circuit. Right Picture: Current travels up to point a where the current is divided through branch containing R1 and branch containing R2. Can someone help me with a general approach for finding Rth? Would it help if I labeled the node voltages and then proceeded on finding Rth? Because I can see that current would not go through R2 because the potential through that branch is zero.