DRAGOMIR, S. S. Some inequalities for the norm and the numerical radius of linear operators in Hilbert spaces. Tamkang Journal of Mathematics, [S. l.], v. 39, n. 1, p. 1-7, 2008. DOI: 10.5556/j.tkjm.39.2008.40. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/40. Acesso em: 21 sep. 2021.