Advances in Difference Equations
Volume 2007 (2007), Article ID 90405, 10 pages
doi:10.1155/2007/90405

On the stability of trigonometric functional equations

Gwang Hui Kim

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

Abstract

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).