The gain on a Non inverting amplifier is 1 + r2/r1
Vout = vin(1+r2/r1)
I'm wondering what the gain will be if r1 is not grounded and is instead connected to v1. Will the gain then be vout=(vin-v1)(1+r2/r1)?
Thanks for your help guys!

 

An opamp will always try to make the sum of the inputs equal to zero. So to tackle this problem use the superposition theorem. http://en.wikipedia.org/wiki/Superposition_theorem
Edit: If you are not student but a self-taught hobbyist I may offer some more help

 

I would think...

Vo=(1+R2/R1)*Vi - (R2/R1)*V1

 

For what it's worth - here's a video that shows a more practical way to think about op amp operation. This approach seems to help many people visualize what an op amp circuit is doing (and what it will do).

https://www.youtube.com/watch?v=K03Rom3Cs28

 

I would think...
Vo=(1+R2/R1)*Vi - (R2/R1)*V1

Yes - and in case Vi=V1 we have a unity gain amplifier - independent on the resistor ratio.
This is a very special circuit that can be used for unity gain operation of an uncompensated operational amplifier.
In this case the feedback factor (that means: the loop gain) can be adjusted for stable operation - independent on the closed loop gain (that always is unity).

 

The gain on a Non inverting amplifier is 1 + r2/r1
Vout = vin(1+r2/r1)
I'm wondering what the gain will be if r1 is not grounded and is instead connected to v1. Will the gain then be vout=(vin-v1)(1+r2/r1)?
Thanks for your help guys!

I can make a reasonable guess as to what you mean by Vout, vin, and r1 and r2.

I have no idea what you could possible mean by v1.

A proper schematic with reference points is required.

 

I can make a reasonable guess as to what you mean by Vout, vin, and r1 and r2.

I have no idea what you could possible mean by v1.

A proper schematic with reference points is required.

Presumably V1 is simply another potential within the common mode range. When V1 is zero volts one has the classic non-inverting amplifier with gain.