Chebyshev polynomials
The Chebyshev polynomials are two sequences of orthogonal polynomials related to the cosine and sine functions, notated as T n ( x ) {\displaystyle T_{n}(x)} and U n ( x ) {\displaystyle U_{n}(x)} . They can be defined in several equivalent ways, one of which starts with trigonometric functions: The Chebyshev polynomials of the first kind T n {\displaystyle T_{n}} are defined by T n ( cos θ ) = cos ( n θ ) .