There are two sets of constants that are commonly known as Lebesgue constants. The first is related to approximation of function via Fourier series, which the other arises in the computation of Lagrange interpolating polynomials. Assume a function f is integrable over the interval [-π, π] and S_n(f, x) is the nth partial sum of the Fourier series of f, so that a_k | = | 1/π integral_(-π)^π f(t) cos(k t) d t b_k | = | 1/π integral_(-π)^π f(t) sin(k t) d t and S_n(f, x) = 1/2 a_0 + { sum_(k = 1)^n[a_k cos(k x) + b_k sin(k x)]}.