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Discrete Dynamics in Nature and Society

Volume 2012 (2012), Article ID 406821, 17 pages

http://dx.doi.org/10.1155/2012/406821

## The Form of the Solutions and Periodicity of Some Systems of Difference Equations

^{1}Mathematics Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia^{2}Department of Mathematics, Faculty of Science, Mansoura University, Mansoura 35516, Egypt

Received 20 May 2012; Accepted 6 July 2012

Academic Editor: Garyfalos Papaschinopoulos

Copyright © 2012 M. Mansour et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

This paper is devoted to get the form of the solutions and the periodic nature of the following systems of rational difference equations , where the initial conditions are real numbers.

#### 1. Introduction

Difference equations appear naturally as discrete analogues and as numerical solutions of differential equations. They have many applications in biology, ecology, economy, and physics. So, recently, there has been an increasing interest in the study of qualitative analysis of rational difference equations and systems of difference equations. Although difference equations are very simple in form, it is extremely difficult to understand thoroughly the behaviors of their solutions, see [1–23] and the references cited therein.

Periodic solutions of a difference equations have been investigated by many researchers, and various methods have been proposed for the existence and qualitative properties of the solution.

The periodicity of the positive solutions of the system of rational difference equations was studied by Çinar in [5].

Elsayed [11] has obtained the solution of the following system of the difference equations: The behavior of the positive solution of the following system: has been studied by Kurbanli et al. [22].

Özban [24] has investigated the positive solution of the system of rational difference equations as Özban [25] has investigated the solution of the following system:

In [26] Yalcinkaya investigated the sufficient condition for the global asymptotic stability of the following system of difference equations: Also, Yalcinkaya [27] has obtained the sufficient conditions for the global asymptotic stability of the system of two nonlinear difference equations as Yang et al. [28] has investigated the positive solution of the system following: Similar nonlinear systems of rational difference equations were investigated [26–41].

In this paper, we investigate the behavior of the solutions of the difference equations systems as where the initial conditions for are real numbers.

#### 2. The First System: ,

In this section, we investigate the solution of the system of two difference equations as where the initial conditions are arbitrary real numbers with , , ,, and , , .

The following theorem is devoted to the form of the solutions of system (2.1).

Theorem 2.1. * Suppose that are solutions of system (2.1). Also, assume that the initial conditions are arbitrary real numbers and let , , , , , , , . Then for , one has
*

*Proof. *For , the result holds. Now suppose that and that our assumption holds for , that is,
Now, it follows from (2.1) that
Similarly, we can prove the other relations.

Lemma 2.2. *Let be a positive solution of system (2.1), then is bounded and converges to zero.*

*Proof. *It follows from (2.1) that
Then, the subsequences , , , , , and are decreasing and so are bounded from above by .

*Example 2.3. *We consider interesting numerical example for the difference system (2.1) with the initial conditions, where, , , , , , , , , , , and (see Figure 1).

#### 3. The Second System: ,

In this section, we study the solution of the following system of the difference equations: where and the initial conditions are arbitrary real numbers such that , , , .

Theorem 3.1. *Assume that are solutions of system (3.1). Then for , one has
*

*Proof. *For , the result holds. Now suppose that and that our assumption holds for , that is,
Now, it follows from (3.1) that
Also, we see from (3.1) that
Similarly, we can prove the other relations.

Lemma 3.2. *The solutions of system (3.1) has unboundedness solutions except in the following case.*

Theorem 3.3. *System (3.1) has a periodic solution of period six if and only if and it will take the form , .*

*Proof. *First suppose that there exists a prime period-six solution
of system (3.1). We see from the form of the solution of system (3.1) that
Then, we get
Thus,
Second, assume that . Then, we see from the form of the solution of system (3.1) that
Thus, we have a periodic solution of period six and the proof is complete.

*Example 3.4. *Figure 2 shows the behavior of the solution of the difference system (3.1) with the initial conditions, where, , , , , , ,,, , , and .

*Example 3.5. *If we consider the difference equation system (3.1) with the initial conditions, where, , , , , , , , , and , then we get the shape of Figure 3.

#### 4. The Third System: ,

In this section, we obtain the form of the solution of the system of two difference equations as where the initial conditions are arbitrary real numbers such that , , , and , , .

Theorem 4.1. * Suppose that are solutions of system (4.1). Then
**
where, , , , , , , ,, , , .*

*Proof. *As the proof of Theorem 2.1, and so it will be omitted.

*Example 4.2. *Figure 4 shows the behavior of the solutions of the system (4.1) with the initial conditions, , , , , , , , , and .

#### 5. The Fourth System: ,

We get, in this section, the solution of the following system of the difference equations: where and the initial conditions are arbitrary real numbers.

Theorem 5.1. *Let be solutions of system (5.1). Then for one has**
where, , , , , , , , , , , .*

*Proof. *For , the result holds. Now suppose that and that our assumption holds for , that is,
It follows from (3.1) that
Then, we see that
Similarly, we can prove the other relations. This completes the proof.

Lemma 5.2. *If , and are arbitrary real numbers and are solutions of system (5.1), then the following statements are true.*(i)*If , , then we have and.*(ii)*If , , then we have and .*(iii)*If , , then we have and .*(iv)*If , , then we have and .*(v)*If , , then we have and .*(vi)*If , , then we have and .*(vii)*If , then we have and .*(viii)*If , then we have and .*(ix)*If , , then we have and .*(x)*If , , then we have and .*(xi)*If , , then we have and .*(xii)*If , , then we have and .*

*Proof. *The proof follows from the form of the solution of system (5.1).

*Example 5.3. *If we take the system of difference equations (5.1) with the initial conditions, , , and , we get the following shape of the solution, see Figure 5.

#### Acknowledgments

This paper was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah. The authors, therefore, acknowledge with thanks the DSR technical and financial support.

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