Briseid, Eyvind, Henrik Forssell, and Bjørn Smestad. “Triangle and Parallelogram Area Formulas: A Critique of Teacher Education Textbooks in Norway”. NOMAD Nordic Studies in Mathematics Education 30, no. 2 (June 30, 2025): 44–67. Accessed December 26, 2025. https://tidsskrift.dk/NOMAD/article/view/162158.