HELFGOTT, Harald; HELFGOTT, Michel. Maxima and minima before calculus. Pro Mathematica, [S. l.], v. 12, n. 23-24, p. 135–158, 1998. Disponível em: https://revistas.pucp.edu.pe/index.php/promathematica/article/view/8133. Acesso em: 19 feb. 2026.