2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/75481In 1970 Nosal gave upper and lower bounds on the sum of the spectral radii of a graph and its complement. We generalize this problem to other eigenvalues and give a number of bounds. We essentially solve the corresponding problem for the second eigenvalues.Combinatorics15A42, 05C50text