S. Sunardi, E. . Yudianto, S. Susanto, . D. . Kurniati, . R. D. . Cahyo, and S. Subanji, “Anxiety of Students in Visualization, Analysis, and Informal Deduction Levels to Solve Geometry Problems”, IJLTER, vol. 18, no. 4, pp. 171–185, Apr. 2019.