On the Brzdȩk’s fixed point approach to stability of a Drygas functional equation in 2-Banach spaces

Using the Brzḑek’s fixed point approach, we will prove the generalized Hyers–Ulam–Rassias stability for the following Drygas functional equation in 2-Banach spaces f(x+y)+f(x-y)=2f(x)+f(y)+f(-y).\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} f(x+y)+f(x-y)=2f(x)+f(y)+f(-y). \end{aligned}$$\end{document}Moreover, we investigate some hyperstability results for this equation.