Advances in Difference Equations
Volume 2007 (2007), Article ID 90405, 10 pages
Research Article

On the Stability of Trigonometric Functional Equations

Gwang Hui Kim

Department of Mathematics, Kangnam University, Youngin, Gyeonggi 446-702, South Korea

Received 17 February 2007; Accepted 5 October 2007

Academic Editor: Bing Gen Zhang

Copyright © 2007 Gwang Hui Kim. 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.


The aim of this paper is to study the superstability related to the d'Alembert, the Wilson, the sine functional equations for the trigonometric functional equations as follows: f(x+y)f(xy)=2f(x)g(y),f(x+y)f(xy)=2g(x)f(y).