Geodesic
On the order of approximation of functions
Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 1 (1992), pp. 90-96 
S. B. Stechkin. On the order of approximation of functions. Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 1 (1992), pp. 90-96. http://geodesic.mathdoc.fr/item/TIMM_1992_1_a6/
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     title = {On the order of approximation of functions},
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Voir la notice du chapitre de livre provenant de la source Math-Net.Ru

It is proved, that results of my paper (On the order of the best approximation of continuous function, Isv. 15 (1951), 219–242) about exact order of approximation of functions by trigonometric polynomials are valid for approximation by more wide class of polynomials, called systems of Bernstein and Jackson.