Fatima N. Ahmed. "Averaging Techniques in The Oscillations of Nonlinear Differential Equations With Alternating Coefficients". مجلة البيان العلمية, no. 14 (نوفمبر 5, 2023): 227–217. تاريخ الوصول ديسمبر 22, 2024. https://journal.su.edu.ly/index.php/bayan/article/view/1838.