Approximate solution of radical quartic functional equation related to additive mapping in 2-Banach spaces

The aim of this paper is first to reformulate the fixed point theorem [4, Theorem 1] in 2-Banach spaces, after it, we introduce and solve the radical quartic functional equationf(x4+y44)=f(x)+f(y). We also show that the fixed point methods allow to investigate Ulam's type stability of radical quartic functional equation in 2-Banach spaces.