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## Homework Statement

I need to derive this expression [itex]v_{out}=\frac{1}{2}(v_{1}-v_{2})(\frac{R_{3}+R_{2}}{R_{3}})[/itex]

Using the circuit I'm given. I uploaded it.

## The Attempt at a Solution

So far I have [itex]v_{in}=v_{+}+v_{-}[/itex] which is from "rule #2 of op amps", which is "The feedback in the op-amp circuit drives the voltage differences between the inverting and non-inverting inputs to zero."

And since the circuit looks like a voltage divider, I can use the voltage divider equation to get [itex]v_{out}=v_{in}(\frac{R_{2}}{R_{1}+R_{2}})[/itex], which gives me [itex]v_{out}=(v_{1}+v_{2})(\frac{R_{2}}{R_{1}+R_{2}})[/itex], but I can't figure out why there's a [itex]\frac{1}{2}[/itex] in front of the equation that I'm given at the beginning, or why the term with the resistors is the inverse of mine.

Thanks.