เฮงคราวิทย์ จ. Functional Equations with Trigonometric Function Solutions. KKU Science Journal, [S. l.], v. 41, n. 3, p. 671–678, 2013. Disponível em: https://ph01.tci-thaijo.org/index.php/KKUSciJ/article/view/249162. Acesso em: 26 aug. 2026.