Fixed Point Theory and Applications
Volume 2008 (2008), Article ID 493751, 9 pages
doi:10.1155/2008/493751
Research Article
Generalized Hyers-Ulam Stability of Quadratic Functional Equations: A Fixed Point Approach
Department of Mathematics, Hanyang University, Seoul 133-791, South Korea
Received 6 September 2007; Revised 19 November 2007; Accepted 15 February 2008
Academic Editor: Thomas Bartsch
Copyright © 2008 Choonkil Park. 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
Using the fixed point method, we prove the generalized Hyers-Ulam
stability of the quadratic functional equation f(2x+y)=4f(x)+f(y)+f(x+y)−f(x−y) in Banach spaces.