I. Muhijah, R. M. M. Sari, R. Zulkarnaen, and K. N. S. Effendi, “The Relationship between Self-Directed Learning and Problem-Solving Ability in Trigonometry”, J.Math.Instr.Soc.Res.Opin., vol. 4, no. 4, pp. 1351–1362, Dec. 2025.