The negative sign indicates that the output is 180 ~ out-of-phase with
the input. The gain is determined solely by the values of the two
resistors. A non-inverting amplifier can likewise be produced by taking
the input to the non-inverting input instead of the inverting input.
As an illustration of the use of an operational amplifier, consider
Figure 1.44 which shows how it can be used as a differential amplifier to