Periodic phenomena occur frequently in many physical and engineering problems.
For example, it occurs in sound waves, flow of heat, electromagnetic waves, mechanical vibrations, motion of earth and the heart under normal conditions. These periodic phenomena are represented by periodic functions which may be complicated. So, it is important to express such general periodic functions in terms of simpler periodic functions, namely, sine and cosine functions.
A representation in the form of a trigonometric series
of sines and cosines was given by the French mathematical physicist Jean Baptiste Joseph Fourier ...