Use the sliders to set the input voltage, Vin, and the gain of the op-Amp, Ao. For this example we will set R1=R2; we will change this later. Since R1 and R2 form a voltage divider, their values don't matter to us, only their ratio.

The resistors R1 and R2 form a voltage divider so $Vn = Vout \cdot \frac{R2}{R1+R2}$.   If we let R1 = R2 (for now), we get $Vn = \frac{Vout}{2}$
We also know the $Vout = Ao \cdot \left( Vp - Vn \right) = Ao \cdot \left( Vin - Vn \right),$
If we substitute the expression for $Vn$ into this expression we get
$Vout = Ao \cdot \left( Vin - \frac{Vout}{2} \right)$. Solving for $Vout$ yields $Vout = Vin \frac{Ao}{1+Ao/2}$

We call the ratio of the output, Vout, to the input, Vp, the gain, G, of the circuit. $G=\frac{Vout}{Vin}=\frac{Ao}{1+Ao/2}$.

Input voltage, Vp = Vin = Volts.
The output voltage is $Vout = Vp \frac{Ao}{1+Ao/2}$ = Volts.
$Vn = \frac{Vout}{2}$ = Volts.

The gain of the circuit is $G=\frac{Vout}{Vin}=\frac{Ao}{1+Ao/2}$ = .