Chebyshev polynomials - Wikipedia
https://en.wikipedia.org/wiki/Chebyshev_polynomialsThe Chebyshev polynomials are two sequences of polynomials related to the cosine and sine functions, notated as and . They can be defined several ways that have the same end result; in this article the polynomials are defined by starting with trigonometric functions: The Chebyshev polynomials of the first kind are given by Similarly, define the Chebyshev polynomials of the second kind as