On the Hyers–Ulam–Rassias stability of an additive functional equation in quasi-Banach spaces

In this paper we investigate the Hyers–Ulam–Rassias stability of the following functional equation:∑i=1mf(mxi+∑j=1,j≠imxj)+f(∑i=1mxi)=2f(∑i=1mmxi) (m∈Nm∈N, m⩾2m⩾2) in quasi-Banach spaces.