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: Sigma(m)(i=1) f(mx(i) + Sigma(m)(j=1, j not equal 1) x(j)) + f(Sigma(m)(i=1)x(i)) = 2f (Sigma(m)(i=1) mx(i)) (m is an element of N, m >= 2) in quasi-Banach spaces. (C) 2008 Elsevier Inc. All rights reserved.