Irawan, Andi, and Edy Surya. “Application of the Open Ended Approach to Mathematics Learning in the Sub-Subject of Rectangular”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 33, no. 3, June 2017, pp. 270-9, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/7539.