In mathematics, a trigonometric series is an infinite series of the form A 0 + ∑ n = 1 ∞ A n cos ⁡ n x + B n sin ⁡ n x, {\displaystyle A_{0}+\sum _{n=1}^{\infty }A_{n}\cos {nx}+B_{n}\sin {nx},} where x {\displaystyle x} is the variable and { A n } {\displaystyle \{A_{n}\}} and { B n } {\displaystyle \{B_{n}\}} are coefficients. Wikipedia