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 ::::Zen-in, you have really stressed me and I still can not realize that you have analyzed this simple circuit with a full screen of formulas while I have done it on one line! The difference between you and me is that you have ""blindly"" analyzed the circuit as a ""black box"" without seeing well-known sub-circuit building blocks. You have done it like a computer (a simulating program) while I have done it like a human being seeing familiar patterns inside the unknown circuit: voltage-to-current converter, current-to-voltage converter, voltage follower, non-inverting amplifier, non-inverting current source... and finally, you can recognize a balanced bridge...  , , email) "