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Cosine-sine functional equation on semigroups

General Mathematics 2023-06-09 v1

Abstract

Let SS be a semigroup. We determine the complex-valued solutions f,g,hf,g,h of the functional equation \begin{equation*}f(xy)=f(x)g(y)+g(x)f(y)+h(x)h(y), x,y\in S,\end{equation*} in terms of multiplicative functions, solutions of the special case φ(xy)=φ(x)χ(y)+χ(x)φ(y),x,yS\varphi(xy)=\varphi(x)\chi(y)+\chi(x)\varphi(y), x,y\in S of the sine addition law, where χ:SC\chi:S\to\mathbb{C} is a multiplicative function, and also in terms of solutions of the particular case ψ(xy)=ψ(x)χ(y)+χ(x)ψ(y)+φ(x)φ(y),x,yS\psi(xy)=\psi(x)\chi(y)+\chi(x)\psi(y)+\varphi(x)\varphi(y), x,y\in S of the cosine-sine functional equation where χ:SC\chi:S\to\mathbb{C} is a multiplicative function and φ:SC\varphi:S\to\mathbb{C} such that the pair (φ,χ)(\varphi,\chi) satisfies the sine addition law.

Cite

@article{arxiv.2306.04666,
  title  = {Cosine-sine functional equation on semigroups},
  author = {Omar Ajebbar and Elhoucien Elqorachi},
  journal= {arXiv preprint arXiv:2306.04666},
  year   = {2023}
}
R2 v1 2026-06-28T10:59:13.221Z