Vebianti, F., S. Sunardi, A. Suwito, D. Trapsilasiwi, and E. Oktavianingtyas. “Analysis of Geometry Problem Solving Based on APOS Theory for Class IX Students”. Journal of Education and Learning Mathematics Research (JELMaR), Vol. 3, no. 1, June 2022, pp. 33-41, doi:10.37303/jelmar.v3i1.69.