Journal of Inequalities and Applications
Volume 2010 (2010), Article ID 184542, 13 pages
doi:10.1155/2010/184542
Research Article

Stability of Approximate Quadratic Mappings

Hark-Mahn Kim, Minyoung Kim, and Juri Lee

Department of Mathematics, Chungnam National University, 79 Daehangno, Yuseong-gu, Daejeon 305-764, South Korea

Received 23 October 2009; Revised 21 January 2010; Accepted 1 February 2010

Academic Editor: Yeol Je Cho

Copyright © 2010 Hark-Mahn Kim 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

We investigate the general solution of the quadratic functional equation f(2x+y)+3f(2x−y)=4f(x−y)+12f(x), in the class of all functions between quasi-β-normed spaces, and then we prove the generalized Hyers-Ulam stability of the equation by using direct method and fixed point method.