1.
Bokayev N, Syzdykova A. An estimate of best approximation by angle of sum of double series with respect to multiplicative system with quasiconvex coefficients . M [Internet]. 2015 Jun. 29 [cited 2025 Dec. 9];2(78):31-6. Available from: https://mts.buketov.edu.kz/mathematics-vestnik/article/view/19