This Demonstration illustrates recovering the Fourier coefficients from a complex wave that you build. With the sliders you can select the weights of five sine wave signals, 1 to 5 Hz. These are summed into a complex signal in the upper graph. You can then selectively choose to multiply the entire output wave by any of the original unweighted signals. When selected, the resultant product waveforms are displayed in the lower graph. When these resultant waveforms are individually integrated or summed, the value of the integral is the original weight applied to the signal (after potentially dealing with scaling issues).