กีรติวิบูลย์ วรางคณา. 2016. “Comparisons of Opinions between Students Unwithdrawn and Withdrawn Calculus 1 of Thaksin University”. KKU Science Journal 44 (1):222-36. https://ph01.tci-thaijo.org/index.php/KKUSciJ/article/view/249492.