On Controllability and Approximate Sturm-Liouville Problems in Time-Varying Second-Order Differential Equations. Contemporary Mathematics , [S. l.], v. 6, n. 5, p. 6496–6511, 2025. DOI: 10.37256/cm.6520255177. Disponível em: https://ojs353.mebyme.cn/index.php/CM/article/view/5177. Acesso em: 24 dec. 2025.