**Turkish Journal of Analysis and Number Theory**

## Some New Wilker and Generalized Lazarević Type Inequalities for Modified Bessel Functions

Département de Mathématiques ISSATK, University of Kairaouan, Kairaouan, TunisiaAbstract | |

1. | Introduction |

2. | Lemmas |

3. | Wilker and Lazarević Type Inequalities for Modified Bessel Functions |

4. | Concluding Remarks |

References |

### Abstract

In this paper our aim is to deduce some new Wilker types inequalities for modied Bessel function of the first kind. In addition, a generalized Lazarević's inequality is established.

**Keywords:** The modified Bessel functions, Wilker type inequalities, Lazarević inequality

Received December 28, 2015; Revised November 19, 2016; Accepted November 29, 2016

**Copyright**© 2016 Science and Education Publishing. All Rights Reserved.

### Cite this article:

- Khaled Mehrez. Some New Wilker and Generalized Lazarević Type Inequalities for Modified Bessel Functions.
*Turkish Journal of Analysis and Number Theory*. Vol. 4, No. 6, 2016, pp 168-171. http://pubs.sciepub.com/tjant/4/6/4

- Mehrez, Khaled. "Some New Wilker and Generalized Lazarević Type Inequalities for Modified Bessel Functions."
*Turkish Journal of Analysis and Number Theory*4.6 (2016): 168-171.

- Mehrez, K. (2016). Some New Wilker and Generalized Lazarević Type Inequalities for Modified Bessel Functions.
*Turkish Journal of Analysis and Number Theory*,*4*(6), 168-171.

- Mehrez, Khaled. "Some New Wilker and Generalized Lazarević Type Inequalities for Modified Bessel Functions."
*Turkish Journal of Analysis and Number Theory*4, no. 6 (2016): 168-171.

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### 1. Introduction

In the literature there are many inequalities satisfied by Bessel and modified Bessel functions of the first kind. Different types of inequalities for this functions are proved, like Turán types inequalities ^{[4, 15]}, Jordan's type Inequalities ^{[5]}, Redheffer's type inequalities ^{[6, 8, 24]}, Huygens types inequalities ^{[10, 11]} and Frame's types inequalities ^{[9]}, ...etc. This paper is a continuation of some inequalities for this functions. Wilker ^{[19]} proposed two open problems:

a. Prove that if then

(1) |

b. Find the largest constant *c* such that

(2) |

for

In ^{[16]}, inequality (1) was proved, and the following inequality:

where the constants and are best possible, was also established.

Wilker-type inequalities (1) and (2) have attracted much interest of many mathematicians and have motivated a large number of research papers involving different proofs and various generalizations and improvements (cf. ^{[3, 23]} and the references cited therein).

In this paper, some new Wilker-type inequalities involving modified Bessel functions of the first kind are established. Moreover, we present a new proof of generalization of the Lazarević and Wilker-type inequalities proved by Baricz ^{[2]}.

Let let us consider the function defined by

(3) |

and is the modified Bessel function of the first kind defined by [^{[18]}, p. 77]

(4) |

It is worth mentioning that in particular we have,

(5) |

(6) |

(7) |

### 2. Lemmas

In order to establish our main results, we need several lemmas, which we present in this section.

Lemma 1. ^{[14]} *Let** ** **and** ** **be real numbers, and let the power series** ** **and** ** **be convergent for** ** **If** ** **for** ** **and if** ** **is strictly increasing (or decreasing) for** ** **then the function** ** **is strictly increasing (or decreasing) on** *

**Lemma 2.** ^{[1, 8, 13]} *Let** ** **be two continuous functions which are di**ff**erentiable on** ** **Further, let** ** **on** ** **If** ** **is increasing (or decreasing) on** ** **then the functions** ** **and** ** **are also increasing (or decreasing) on *

### 3. Wilker and Lazarević Type Inequalities for Modified Bessel Functions

The first aim of this paper is to prove the following inequalities.

**Theorem 1. ***Let** ** **the following inequalities*

(8) |

*and*

(9) |

holds for all

*Proof.* Let we define the function on by

where and

By using the differentiation formula [^{[18]}, p. 79]

(10) |

we can easily show that

(11) |

and

(12) |

Thus

(13) |

Using the Cauchy product

(14) |

we get

where

(15) |

and

(16) |

Now, we define the sequence for thus

We conclude that is increasing for and is also increasing on by Lemma 1. Thus

(17) |

is increasing on by Lemma 2. Furthermore,

from which follows the inequality (8) holds for all and Finally, using the the arithmeticgeometric mean inequality and equality (9), we get

(18) |

Since the inequality (9) holds for all and So, the proof of Theorem 1 is complete.

In this theorem, we establish new inequalities of the Wilker type for modified Bessel function of the first kind.

**Theorem 2**. *Let** **and** ** **the following Wilker type inequality*

(19) |

*is valid. In particular, the following inequality*

(20) |

hold for all

*Proof.* We define the function on by

The Mittag-Leffler expansion for the modified Bessel functions of first kind, which becomes [^{[7]}, Eq. 7.9.3]

(21) |

where are the positive zeros of the Bessel function , and the differentiation formula (10) we have

Thus implies that the function is increasing on for all and consequently for all So, the following inequality

(22) |

holds for all and . By using the arithmetic-geometric mean inequality we obtain

Finally, Observe that using (5) and (6) in particular for we obtain the inequality (20).

In the next theorem we present a generalization of the Lazarević and Wilker-type inequalities to modified Bessel functions of the first kind. The next result exist in ^{[3]}. We give an elementary proof.

**Theorem 3.** *let** ** **and** ** **Then, the following inequalities*

(23) |

*and*

(24) |

*holds if and only if** *

*Proof*. Let where and From the differentiation formula (10) we get

where

and

We define the sequence by for thus implies that

and consequently is decreasing for so the function is decreasing on by Lemma 1. Thus is decreasing on by Lemma 2. Now,

Therefore, (23) holds. From arithmetic-geometric mean inequality and inequality (23), we have

and the proof of theorem is complete.

### 4. Concluding Remarks

1. In proof of Theorem 1, we can see that the following Turán type inequality

(25) |

holds for all and This inequality is not new and it is actually equivalent to a very well-known Turán type inequality for the modified Bessel function of the first kind, firstly discovered by Thiruvenkatachar and Nanjundiah, see ^{[17]}

2. On the other hand, by using (5), (6) and (7) in particular for the Turán type inequality (25) becomes

3. Inequality (23) is a natural generalization of the Lazarević inequality [^{[12]}, p. 207]

(26) |

where Recently, Zhu gives a new proof of the inequality (26) in ^{[20]} and extends the inequality (26) to the following result in ^{[21]} by: for and , then

(27) |

holds if and only if Moreover, in ^{[22]}, Zhu gives another generalization of the inequality (26) as follows: for or then

(28) |

holds if and only if

### References

[1] | G.D. Anderson, S.-L. Qiu, M.K. Vamanamurthy, M. Vuorinen, Generalized elliptic integral and modular equations, Pacific J. Math. 192 (2000) 137. | ||

In article | View Article | ||

[2] | Á. Baricz, Functional inequalities involving Bessel and modified Bessel functions of the first kind, Expo. Math. 26 (2008) 279 293. | ||

In article | View Article | ||

[3] | Á. Baricz, J. Sndor, Extensions of the generalized Wilker inequality to Bessel functions.J.Math.Inequal. 2(3),397-406 (2008). | ||

In article | View Article | ||

[4] | Á. Baricz, Bounds for Turnians of modified Bessel functions, Expo. Math. 33(2) (2015) 223251. | ||

In article | View Article | ||

[5] | Á. Baricz, Jordan-type inequalities for generalized Bessel functions. J. Inequal. Pure Appl. Math. 9(2) (2008), Article 39, 6 pp. (electronic). | ||

In article | |||

[6] | Á. Baricz, Redheffer type inequality for Bessel functions. J. Inequal. Pure Appl. Math. 8(1) (2007), Article 11, 6 pp. (electronic). | ||

In article | |||

[7] | A. Erdélyi, W. Magnus, F. Oberhettinger, F. Tricomi, Higher transcendental Functions, vol. 2, McGraw-Hill, New York, 1954. | ||

In article | PubMed | ||

[8] | K. Mehrez, Redheffer type Inequalities for modified Bessel functions, Arab. Jou. of Math. Sci. 2015. | ||

In article | PubMed | ||

[9] | K. Mehrez, Extension of Frame's type inequalities to Bessel and modified Bessel functions, arXiv. | ||

In article | |||

[10] | K. Mehrez, Extension of Huygens type inequalities for Bessel and modified Bessel functions of the first kind, arXiv.1601. | ||

In article | |||

[11] | K. Mehrez, Generalized Huygens types inequalities for Bessel and modified Bessel functions, arXiv:1601.01007v1. | ||

In article | |||

[12] | D.S. Mitrinović, Analytic Inequalities, Springer, Berlin, 1970. | ||

In article | View Article | ||

[13] | I. Pinelis, Non-strict l'Hospital-type rules for monotonicity: intervals of constancy, J. Inequal. Pure Appl. Math. 8 (1) (2007). article 14, 8 pp.,(electronic). | ||

In article | |||

[14] | S. Ponnusamy, M. Vuorinen, Asymptotic expansions and inequalities for hypergeometric functions, Mathematika 44 (1997) 278301. | ||

In article | View Article | ||

[15] | J. Segura, Bounds for ratios of modified Bessel functions and associated Turn-type inequalities, J. Math. Anal. Appl. 374 (2) (2011) 516. | ||

In article | View Article | ||

[16] | J. S. Sumner, A. Jagers, M. Vowe, J. Anglesio, Inequalities involving trigonometric functions, The American Mathematical Monthly, 98, (3) (1991), 264267. | ||

In article | |||

[17] | [V.R. Thiruvenkatachar, T.S. Nanjundiah, Inequalities concerning Bessel functions and orthogonal polynomials, Proc. Ind. Acad. Sci. Sect. A 33 (1951) 373-384. | ||

In article | |||

[18] | G.N. Watson, A Treatise on the Theory of Bessel Functions, Cambridge University Press, 1922. | ||

In article | |||

[19] | J.B. Wilker, Problem E3306.Am.Math.Mon.96(1),55(1989). | ||

In article | |||

[20] | L. Zhu, On Wilker-type inequalities, Math. Ineq. and App., vol. 10, no. 4, pp. 727 731, 2007. | ||

In article | |||

[21] | L. Zhu, Generalized Lazarevic's inequality and its applications, part I, submitted. | ||

In article | |||

[22] | L. Zhu, Generalized Lazarevic's inequality and its applications, part II, Journal of Inequalities and Applications Volume 2009, 4. pp. | ||

In article | |||

[23] | L. Zhu, Inequalities for hyperbolic functions and their applications. J.Inequal.Appl.2010, Article ID 130821(2010). | ||

In article | View Article | ||

[24] | L. Zhu and J. Sun: Six new Redheffer-type inequalities for circular and hyperbolic func- tions. Comput. Math. Appl. 56(2) (2008), 522-529. | ||

In article | View Article | ||