Al-Btoush, Rateb, and Al-Oushoush Nizar Kh.Kh. “APPROXIMATION OF CONTIONUOUS FUNCTIONS BY VALLEE-POUSSIN’S SUMS”. Italian Journal of Pure and Applied Mathematics, vol. 37, Jan. 2017, pp. 541-52, https://journals.uniurb.it/index.php/ijpam/article/view/6680.