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I understand the circuit to be a summing circuit but I am struggling to analyse past this point: Vout = R5 (((-R2/R1 * V2)/R4) * (V1 / R3)). can anyone analyse this further to prove that R5 is the controlling resistor?

schematic

simulate this circuit – Schematic created using CircuitLab

mwilliams25
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  • So, what is your precise question? – Marcus Müller Nov 18 '19 at 13:12
  • I need help in proving which resistor controls the gain of the whole circuit – mwilliams25 Nov 18 '19 at 13:14
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    That's still a statement, and not a question! I know this really sounds like nitpicking, but since this is clearly a homework-style assignment, we'd really need to know what you've considered so far to be able to help you– and we **really** need you to ask a question to have something specific to answer. – Marcus Müller Nov 18 '19 at 13:16
  • (it helps when you add that to the question instead of as a comment - this is crucial!) – Marcus Müller Nov 18 '19 at 13:18
  • Forget equations for a second and think about what you're looking at. OA1, R1 and R2 are a inverting amplifier. Next you have a summing amplifier which adds V1 and the output from the last opamp. If you only had the OA1 circuit, and I asked you which resistor set the gain what would you say? If I asked the same question for just OA2, what would you say? Now ignore OA1, redraw the circuit with just Vx and V1. What resistor sets the gain then? – user187594 Nov 18 '19 at 13:32

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