Stability of a functional equation deriving from quadratic and additive functions in quasi-Banach spaces

摘要

In this paper we establish the general solution of the functional equation f(2x+y)+f(2x-y)=f(x+y)+f(x-y)+2f(2x)-2f(x) and investigate the Hyers–Ulam–Rassias stability of this equation in quasi-Banach spaces.