Berrehail CE, Bouslah Z. Study of Periodic Solutions for a Ninth-Order Non-Autonomous Differential Equation Using First-Order Averaging Theory. JAND [Internet]. 2026 Sep. 1 [cited 2026 Oct. 17];15(3):723-38. Available from: https://lhscientificpublishing.com/index.php/jand/article/view/293