Question

Design an operational amplifier circuit with an output voltage of the form v=k(v1-v2-v3) where v1, v2 and v3 are the input voltages into the input terminals 1,2 and 3 respectively.

Answer 1

Is this supposed to be done with one OpAmp? It can be easily done with three-
v2, v3 into a summer OpAmp, invert, then into a summer OpAmp with v1 that has a gain of k.
Of course all OpAmp having appropriate bias circuit to eliminate offsets.

Answer 2

It should be done with three,please show me how it's done.

Answer 3

Actual the gain is - for op amp in this mode, therefore center op amp should be placed at end. R2 ~ R||R||R to minimize current offset, Rp and R1 should be selected to span voltage offset.