Heljiu, Marius. “Double Inequalities for Quadrature Formula of Gauss Type”. Rev. Anal. Numér. Théor. Approx. 40, no. 2 (August 1, 2011): 156–163. Accessed April 11, 2025. https://ictp.acad.ro/jnaat/journal/article/view/2011-vol40-no2-art6.