input voltage for op amp


Joined Jun 6, 2011
There is nothing to "prove". This is by definition for an op amp operating closed loop. Actually, there will be a small difference (ignoring input offset voltage) due to the finite open loop gain. The difference * (open-loop gain) = output. The open-loop gain is usually so large that it can be ignored in most cases, and the assumption that in+ = in- is valid.