Perwitasari, Dewi, and Edy Surya. “The Development of Learning Material Using Problem Based Learning to Improve Mathematical Communication Ability of Secondary School Students”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 33, no. 3 (June 3, 2017): 200–207. Accessed May 7, 2024. https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/7382.