MAYANG SARI. Student’s Understanding of Concepts Based on APOS Theory on the material of triangles and quadrilaterals in terms from the level of mathematical ability. Center of Education Journal (CEJou), [S. l.], v. 5, n. 1, 2025. DOI: 10.55757/cejou.v5i1.606. Disponível em: https://ejournal.unupasuruan.ac.id/index.php/cejou/article/view/606. Acesso em: 12 oct. 2026.