Vakarchuk SB. On the Best Polynomial Approximations of $2π$-Periodic Functions and Exact Values of $n$-Widths of Functional Classes in the Space $L_2$. Ukr. Mat. Zhurn. [Internet]. 2002Dec.25 [cited 2024Nov.22];54(12):1603-15. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/4199