1. A trigonometric functional equation with an automorphism.
- Author
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Aserrar, Youssef, Elqorachi, Elhoucien, and Rassias, Themistocles M.
- Subjects
FUNCTIONAL equations ,TRIGONOMETRIC functions ,AUTOMORPHISMS ,SEMIGROUPS (Algebra) ,GENERALIZATION - Abstract
Let S be a semigroup. In the present paper, we determine the complex-valued solutions (f, g) of the functional equation g(xσ(y)) = g(x)g(y) − f(x)f(y) + αf(xσ(y)), x, y ∈ S, where σ : S → S is an automorphism that need not be involutive, and α ∈ C is a fixed constant. Our results generalize and extend the ones by Stetkær in The cosine addition law with an additional term. Aequat Math., no. 6, 90, 1147-1168 (2016), and also the ones by Aserrar and Elqorachi in A generalization of the cosine addition law on semigroups. Aequat Math. 97, 787–804 (2023). Some consequences of our results are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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