Oscillation and nonoscillation of second order differential equations with delay depending on the unknown function

Oscillation and nonoscillation of the second order differential equation with delay depending on the unknown function ( r ( t ) x ′ ( t ) ) ′ + f ( t , x ( t ) , x ( ▵ ( t , x ( t ) ) ) ) = 0 in the case when ∫ ∞ d s / r ( s ) < ∞ holds are consider. The results obtained in this paper can be conjugated with the theorems given by Bainov et al. [J. Comput. Appl. Math. 91 (1998) 87–96].