Harmonic analysis is a branch of mathematics that studies the representation of functions or signals as a sum of basic trigonometric functions, such as sine and cosine waves. It involves the analysis of periodic functions, Fourier series, Fourier transforms, and other mathematical tools for analyzing and decomposing complex signals into simpler components. Harmonic analysis has applications in many areas, including signal processing, engineering, physics, and music theory. It is used to analyze and process signals in various applications, such as image and sound processing, telecommunications, and control systems. Additionally, harmonic analysis plays a key role in understanding and solving differential equations, as well as in studying the properties of different types of functions.