Hyers–Ulam Stability Results for a Functional Inequality of s , t -Type in Banach Spaces

Abstract

We introduce an additive $\left(s,t\right)$ -functional inequality where $s$ and $t$ are nonzero complex numbers with $\sqrt{2}\left|s\right|+\left|t\right|<1.$ Using the direct method and the fixed point method, we give the Hyers–Ulam stability of such functional inequality in Banach spaces.