Copyright © 2010 M. Eshaghi Gordji and H. Khodaei. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Th. M. Rassias (1984) proved that the norm defined over a real vector space X is induced by an inner product if and only if for a fixed integer n≥2,  ∑i=1n∥xi-(1/n)∑j=1nxj∥2=∑i=1n∥xi∥2-n∥(1/n)∑i=1nxi∥2 holds for all x1,…,xn∈X. The aim of this paper is to extend the applications of the fixed point alternative method to provide a fuzzy stability for the functional equation ∑i=1nf(xi-(1/n)∑j=1nxj)=∑i=1nf(xi)-nf((1/n)∑i=1nxi) which is said to be a functional equation associated with inner product spaces.