Hyperstability of some functional equations in modular spaces

Abstract

In this paper, we investigate some hyperstability results, inspired by the concept of Ulam stability, for the following functional equations: \begin{equation} φ(x+y)+φ(x-y)=2φ(x)+2φ(y) \end{equation} \begin{equation} φ(ax+by) = Aφ(x)+Bφ(y)+C \end{equation} \begin{equation}\label{eqnd} f\left(\sum_{i=1}^{m}x_{i}\right)+\sum_{1\leq i<j\leq m}f\big(x_{i}-x_{j}\big)=m\sum_{i=1}^{m}f(x_{i}) \end{equation} in modular spaces.