Geodesic
On constants in the Jackson–Stechkin theorem in the case of approximation by algebraic polynomials
Informatics and Automation, Harmonic analysis, approximation theory, and number theory, Tome 303 (2018), pp. 26-38 
A. G. Babenko; Yu. V. Kryakin. On constants in the Jackson–Stechkin theorem in the case of approximation by algebraic polynomials. Informatics and Automation, Harmonic analysis, approximation theory, and number theory, Tome 303 (2018), pp. 26-38. http://geodesic.mathdoc.fr/item/TRSPY_2018_303_a2/
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     author = {A. G. Babenko and Yu. V. Kryakin},
     title = {On constants in the {Jackson{\textendash}Stechkin} theorem in the case of approximation by algebraic polynomials},
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     pages = {26--38},
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     volume = {303},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TRSPY_2018_303_a2/}
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Voir la notice de l'article provenant de la source Math-Net.Ru

New estimates are proved for the constants $J(k,\alpha )$ in the classical Jackson–Stechkin inequality $E_{n-1}(f) \le J(k, \alpha ) \omega _k (f,{\alpha \pi }/{n})$, $\alpha >0$, in the case of approximation of functions $f \in C[-1,1]$ by algebraic polynomials. The main result of the paper implies the following two-sided estimates for the constants: $1/2\le J(2k,\alpha )<10$, $n \ge 2k(2k-1)$, $\alpha \ge 2$.

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