This document discusses Fourier series and their application to even and odd functions. It introduces Fourier series and their use in decomposing periodic functions into harmonic components. It then explains that for even functions, the Fourier coefficients bn are zero and an can be determined from the integral of the function times cosine from 0 to π. For odd functions, the Fourier coefficient a0 is zero and bn can be determined from the integral of the function times sine from 0 to π. The document concludes that Fourier series have important applications in civil engineering for solving vibration problems such as determining earthquake frequencies.