VAKARCHUK, S. B. On the Best Polynomial Approximations of $2π$-Periodic Functions and Exact Values of $n$-Widths of Functional Classes in the Space $L_2$. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 54, n. 12, p. 1603–1615, 2002. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4199. Acesso em: 27 apr. 2025.