On the stability of radical functional equation in modular space

Abstract

In this work, we prove the generalised Hyer Ulam stability of the following functional equation \begin{equation}\label{Eq-1} ϕ(x)+ϕ(y)+ϕ(z)=q ϕ\left(\sqrt[s]{\frac{x^s+y^s+z^s}{q}}\right),\qquad |q| \leq 1 \end{equation} and $s$ is an odd integer such that $s\ge 3$, in modular space, using the direct method, and the fixed point theorem.