*Article* **Improved Conditions for Oscillation of Functional Nonlinear Differential Equations**

**Omar Bazighifan 1,2,† and Mihai Postolache 3,4,5,***<sup>∗</sup>***,†**


Received: 17 March 2020; Accepted: 3 April 2020; Published: 9 April 2020

**Abstract:** The aim of this work is to study oscillatory properties of a class of fourth-order delay differential equations. New oscillation criteria are obtained by using generalized Riccati transformations. This new theorem complements and improves a number of results reported in the literature. Some examples are provided to illustrate the main results.

**Keywords:** oscillatory solutions; nonoscillatory solutions; fourth-order; delay differential equations; riccati transformation
