Goodarzi, Khodayar, and M. Nadjafikhah *. “λ-Symmetry and Integrating Factor For X ̈(f(t,x)+g(t,x)x ̇)e^x: Mathematics, Symmetry”. Hyperscience International Journal 2, no. 1 (March 10, 2022): 7–13. Accessed July 18, 2024. https://hscience.org/index.php/hij/article/view/14.