Papers published in the English version of the journal

A Note on the Approximation by a Sum of Two Algebras

A. Kh. Askarova^ab, V. È. Ismailov<sup>ac

a</sup> Institute of Mathematics and Mechanics, Azerbaijan National Academy of Sciences, Baku
^b Khazar University, Department of Mathematics
^c Khazar University

Abstract: We consider the problem of approximation of a continuous function $f$ defined on a compact metric space $X$ by elements from a sum of two algebras. We prove a de la Vallée Poussin type theorem, which estimates the approximation error $E(f)$ from below. We also obtain a duality formula for the precise computation of $E(f)$.

Keywords: de la Vallée Poussin theorem, approximation error, bolt, duality formula.

Received: 22.11.2024
Revised: 22.11.2024

Language: English

 English version: Mathematical Notes, 2025, 118:3, 442–449

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