PACHPATTE, B. G. On approximate solutions of a certain hyperbolic partial differential equation. **Tamkang Journal of Mathematics**, *[S. l.]*, v. 42, n. 1, p. 95–104, 2011. DOI: 10.5556/j.tkjm.42.2011.869. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/869. Acesso em: 28 may. 2023.