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### Operational Amplifier as Differential Amplifier

__Derivation of the equation for the output voltage considering that all 4 resistors R1 to R4 are of different values:__

Case: V_{IN1}= 0 and thus V_{i-}= 0:Calculation of V

_{i+}via voltage divider:For the partial output voltage V

_{OUT+ }you get:Eq. (1) in Eq. (2) results in

Case: V

_{IN2}= 0 and therefore V_{i+}= 0:Bringing together equations (3) and (4):

**If the input voltage in both inputs should be acquired in the same way:**

The symmetry of the resistors must be right, i.e. the resistance ratios R1=R2 and R3=R4 must apply so that the operational amplifier, as a differential amplifier, acquires the same voltages at its inputs in the same way: