Journal of Inequalities and Applications
Volume 2010 (2010), Article ID 635720, 15 pages
doi:10.1155/2010/635720
Research Article

Stability of Quadratic Functional Equations via the Fixed Point and Direct Method

Eunyoung Son, Juri Lee, and Hark-Mahn Kim

Department of Mathematics, Chungnam National University, Daejeon 305-764, South Korea

Received 13 October 2009; Accepted 19 January 2010

Academic Editor: Yeol Je Cho

Copyright © 2010 Eunyoung Son et al. 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

Cădariu and Radu applied the fixed point theorem to prove the stability theorem of Cauchy and Jensen functional equations. In this paper, we prove the generalized Hyers-Ulam stability via the fixed point method and investigate new theorems via direct method concerning the stability of a general quadratic functional equation.