voltage - How do I calculate the gain of an op-amp summing amplifier?

So if I have a summing amplifier circuit like the one below:

I know the Vin1, Vin2, and Vout value and the circuit is designed such that Vout = -(Vin1+2Vin2) but how do I calculate the gain? I know on a normal op-amp circuit with one input source the gain is just Vout/Vin. But if I have two input sources then will my gain be Vout/(Vin1+Vin2)?

On PSPICE I set the DC and ACMAG values for the input voltages to 2V, and Vout is -6. So it works out right, but still what is the gain?

Answer

Gain is set for each \$ V_{in} \$.

\$ A_{Vin1} = -\dfrac{R_3}{R_1}\$.

\$ A_{Vin2} = -\dfrac{R_3}{R_2}\$.

and so on, \$ A_{Vin N} = -\dfrac{R_3}{R_N}\$.

If you were to analyze this circuit using superposition, you would find that for each input signal, it is just an inverting amplifier. The signals are amplified or attenuated individually. Therefore, gain is only a meaningful quantity with respect to each individual signal. Since gains are all independent of each other, summing them does not yield a meaningful result.