(Rapeepat Kaewam) ร. แ. “DEVELOPING OF LEARNING ACTIVITIES FOCUSING ON MATHEMATICAL CONNECTION USE PROBLEM-BASED LEARNING FOR GRADE 9 STUDENTS”. Journal of Education and Innovation, vol. 19, no. 4, Jan. 2018, pp. 214-22, https://so06.tci-thaijo.org/index.php/edujournal_nu/article/view/108456.