Journal of Inequalities and Applications
Volume 2009 (2009), Article ID 193035, 19 pages
doi:10.1155/2009/193035
Research Article

Fixed Points and Stability of a Generalized Quadratic Functional Equation

Abbas Najati1 and Choonkil Park2

1Department of Science, University of Mohaghegh Ardabili, Ardabil 51664, Iran
2Department of Mathematics, Hanyang University, Seoul 133-791, South Korea

Received 26 November 2008; Revised 24 January 2009; Accepted 11 February 2009

Academic Editor: Patricia J. Y. Wong

Copyright © 2009 Abbas Najati and 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 generalized quadratic functional equation f(rx+sy)=r2f(x)+s2f(y)+(rs/2)[f(x+y)−f(x−y)] in Banach modules, where r,s are nonzero rational numbers with r2+s2≠1.