This Demonstration shows the response of a low-pass RC filter to one of three user-selectable input waveforms: sine wave, square wave, and triangular wave. The RC filter is a series interconnection of a resistor and capacitor, with the output voltage measured across the capacitor. The results were obtained by solving the first-order differential equation, , where and are output and input voltages, respectively, is the unit step function, and and are the resistor and capacitor. For normalization purposes, the resistor and capacitor are assumed to have unit values. The capacitor is assumed to be discharged, resulting in the initial condition .