By using an exact estimate for approximation by known trigonometric polynomials, we strengthen a Jackson-type theorem. Moreover, we determine the exact order of approximation of some periodic functions by these polynomials. For this purpose, we introduce a special modulus of smoothness.
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Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, No. 7, pp. 954–969, July, 2012.
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Kotova, O.V., Trigub, R.M. Exact order of approximation of periodic functions by one nonclassical method of summation of Fourier series. Ukr Math J 64, 1090–1108 (2012). https://doi.org/10.1007/s11253-012-0701-6
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DOI: https://doi.org/10.1007/s11253-012-0701-6