STRONG APPROXIMATION BY FOURIER-LAPLACE SERIES ON THE UNIT SPHERE Sn − 1.

We study the strong approximation properties of the Cesáro means of order δ of the Fourier-Laplace expansion of functions integrable on the unit sphere Sn-1, where δ &gT; λ := (n - 2)/2, the latter being the critical index for Cesáo summability of Fourier-Laplace series on Sn-1. The main purpose of this paper is to extend known results from the unit circle S1 to the general sphere Sn-1 with n &gT; 3. We prove six theorems. To prove Theorems 1–3, our machinery is based on the equieonvergent operator ENδ(f) of the Cesáro means σNδ (f) on Sn-1 introduced by Wang Kunyang for δ > -1. We prove in Theorem 6 that ENδ(f) is also equiconvergent with σNδ(f) for δ > 0 in the case of strong approximation. To prove Theorems 4 and 5, we rely on known equivalence relations between K-functionals and moduli of continuity. [ABSTRACT FROM AUTHOR]