This document discusses Fourier series representation of signals. It defines orthogonal sets and explains that any signal can be represented as a combination of orthogonal basis functions using Fourier series. There are two common ways to represent a signal using Fourier series: using trigonometric or exponential basis functions. An example signal is represented using both trigonometric and exponential Fourier series. The magnitude and phase spectra of the example signal are also calculated from the Fourier series coefficients.