Soleha, A. “Improving Activity and Learning Outcomes by Using Contextual Teaching Learning (CTL) With Van Hiele Theory”. Jurnal Axioma : Jurnal Matematika Dan Pembelajaran, vol. 2, no. 2, July 2017, pp. 197-05, https://ejurnal.uij.ac.id/index.php/AXI/article/view/302.