Hi,
Now two new resistors.
They make things complicated, because they involve new source impedance, that needs to be added to the input resistance R1.
Additionally the suming_point_voltage depends on the other input voltages.
The more simple circuit is the usual (inverting) suming amplifier, where all the input resistors are connected to the inverting_Opamp_input..(which usually has a constant voltage = 0V).
But at first give unambiguous informations:
This can be a complete formula like
V_out = A1 x V_in1 + A2 x 1.2V (replace A1 and A2 with your desired values)
Or give clear informations for different input situations, like:
Situation1:
* V_in1 = xxx V
* V2 = 1.2 V (as far as I understand this is always the case. Please correct, if necessary)
* Expected Vout = yyyy V
Situation2:
* V_in1 = xxx V
* V2 = 1.2 V
* Expected Vout = yyyy V
A simple situation for calculation is V_in1 = 0V..
Klaus