Stability of the Cosine-Sine Functional Equation on amenable groups

Ajebbar Omar, Elqorachi Elhoucien

In this paper we establish the stability of the functional equation \begin{equation*}f(xy)=f(x)g(y)+g(x)f(y)+h(x)h(y),\;x,y\in G,\end{equation*} where $G$ is an amenable group.