Opamp_ as a Subractor & Adder

The input signal is in the inverting input of the OpAmp. The non-inverting input of the OpAmp is connected to the reference potential - ground. The inverting amplifier inverts the signal (shifts in phase by 180 °) and increases / reduces voltage, i.e. multiplies voltage to a negative constant: Vout=-Vin*(R2/R1). The gain of the scheme is -R2/R1. The gain can take absolute values grater or smaller than 1. The input resistance is: Rin=R1. The output resistance is: Rout=0.