On L_{1}-Convergence\\ of the r-th Derivative of Cosine Series\\ with r-quasi convex coefficients


We study L_{1}-convergence of r-th derivative of modified cosine sums introduced in \cite{BN}. Exactly it is proved the  L_{1}- convergence of r-th derivative of  modified  cosine   sums with r-quasi convex coefficients.

DOI Code: 10.1285/i15900932v30n2p113

Keywords: cosine sums; L1-convergence; r-quasi convex null sequences

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