Resumen: In this paper, we obtain L 1-weighted norms of classical orthogonal polynomials (Hermite, Laguerre and Jacobi polynomials) in terms of the zeros of these orthogonal polynomials; these expressions are usually known as quadrature rules. In particular, these new formulae are useful to calculate directly some positive defined integrals as several examples show. Idioma: Inglés Año: 2016 Publicado en: Mediterranean Journal of Mathematics 13, 3 (2016), 1291-1306 ISSN: 1660-5446 Factor impacto JCR: 0.868 (2016) Categ. JCR: MATHEMATICS rank: 83 / 310 = 0.268 (2016) - Q2 - T1 Categ. JCR: MATHEMATICS, APPLIED rank: 138 / 255 = 0.541 (2016) - Q3 - T2 Factor impacto SCIMAGO: 0.655 - Mathematics (miscellaneous) (Q2)