On the stability of trigonometric functional equations

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 (x - y) = 2f (x)g(y), f (x + y) - f (x - y) = 2g(x) f (y).Copyright (c) 2007.