Z. A. Abdullah, “Solution of Nonlinear Ordinary Delay Differential Equations Using Variational Approach”, Al-Nahrain J. Sci., vol. 15, no. 4, pp. 183–187, Dec. 2012, Accessed: May 22, 2026. [Online]. Available: https://anjs.edu.iq/index.php/anjs/article/view/618