Hi friends!
I saw in AAC in the page http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/the-instrumentation-amplifier/
that the formula for the potential difference in the below circuit between the two points 3 and 4 is

.

But I have a doubt in the formula that instead of v2-v1, it must be v1-v2??
Am I correct?

 

The only difference between the equation and your question is a - sign. The equation is correct as stated because V2 is the non-inverting input for the overall circuit, and the standard way of describing amplifier gain is the non-inverting input minus the inverting input.

ak

 

The only difference between the equation and your question is a - sign. The equation is correct as stated because V2 is the non-inverting input for the overall circuit, and the standard way of describing amplifier gain is the non-inverting input minus the inverting input.

ak

That's what I have stated

 

Actually, there is a minor error, but not the one you stated. The equation V3-4 = ... should be V4-3 = ...

ak

 

it must be v1-v2??
Am I correct?

Yes.