Luzano, J. F. “Development and Validation of Strategic Intervention Materials (SIMs) of the Selected Topics in Trigonometry of Precalculus Discipline in Senior High School”. Journal of Mathematics and Statistics Studies, vol. 1, no. 2, Dec. 2020, pp. 26-37, https://al-kindipublisher.com/index.php/jmss/article/view/752.