الفهرس 
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Abstract
In recent decades much studies activity has been don regarding the oscillation of solutions of delay differential equations. The main objective of this thesis is to shed light on many equations of fourth and higher order, through studying the behavior of solutions of those equations by different methods and comparison of results. Thesis’/ dissertation’ summary : Content of the thesis/ the dissertation is in (5) chapters as follow : Chapter 1. This chapter is an introductory chapter and it contains some basic definitions, elementary results. Chapter 2. In this chapter, the student studied the asymptotic behavior of solutions of a class of fourth-order nonlinear neutral differential equation with deviating arguments. Chapter 3. By using Riccati transformation technique and comparison theorems the student is concerned with the oscillation of solutions of even-order neutral differential equations. Also, on the other hand, this chapter deals with the oscillation and behavior of solutions of even-order nonlinear neutral differential equation with several deviating arguments. Chapter 4. This chapter discusses asymptotic behavior of solutions of higher-order nonlinear differential equations with distributed delay. More precisely, the student will establish some sufficient conditions which insure that any solution oscillates. Chapter 5. In this chapter, the student are concerned with the oscillation of solutions of a class of fourth order nonlinear differential equations with middle term.