Oscillation criteria of second order differential equations with positive and negative coefficients

In this paper we obtain oscillation criteria for solutions of homogeneous and nonhomogeneous cases of second order neutral differential equations with positive and negative coefficients. Our results improve and extend the results of [Oscillation criteria for a class of second order neutral delay differential equations, Appl. Math. Comput. \textbf{210}, 303--312, 2009].