On the issue of expanding this function into a series in Jacobi polynomials

Abstract

The purpose of this note is to simplify the method proposed by academician N. M. Krylov for constructing a given function in the form of a series acting in Jacobi polynomials. By forming an a priori expansion with uniform and absolute convergence, we show, without relying on the Riesz-Fischer theorem, that it can be identified with expansions in Jacobi polynomials.