1. The problem statement, all variables and given/known data Why are the two circuits below equivalent? 2. Relevant equations N/A 3. The attempt at a solution Background: I am studying BJTs, and in my textbook the equivalent resistance of resistor 1 and 2 is noted to be in parallel. The text provides no explanation why. In my search for an explanation I stumbled upon a video from David Williams (https://goo.gl/VCCuCy) where he redraws the circuit on the left. Once it is in the form on the right I can identify why the resistors are in parallel, but I do not understand how Mr. Williams redrew the circuit. I would greatly appreciate if someone could walk me through their thought process. For now I can simply remember to do that transformation, but I want to understand the fundamentals so I can apply that technique to different circuits. If my usage of the terms transformation and equivalent are incorrect for this case please let me know.