The application of Brzdek's fixed point theorem in the stability problem of the Drygas functional equation

Authors: MEHDI DEHGHANIAN, YAMIN SAYYARI

Abstract: Using the Brzdek fixed point theorem, we establish the Hyers?Ulam stability problem of Drygas functional equations \begin{equation} \delta(x+y-z)+\delta(x-y)+\delta(-y-z)+\delta(y)=\delta(x-y-z)+\delta(y-z)+\delta(x+y)+\delta(-y)\nonumber \end{equation} for all $x,y,z\in A$.

Keywords: Brzdek fixed point theorem, Drygas functional equation, stability

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