If there are two inputs to the inverting input of the op amp,
as shown in Figure 1, then it will behave as a summing amplifier, the output being an amplification of the
sum of the two inputs. Using the symbols shown it can be proved
that:
Output of a summing amplifier (Vo) = - R3(V1/R1 + V2R2)
A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS CD