- Research Article
- Open access
- Published:
A Hilbert's Inequality with a Best Constant Factor
Journal of Inequalities and Applications volume 2009, Article number: 820176 (2009)
Abstract
We give a new Hilbert's inequality with a best constant factor and some parameters.
1. Introduction
If , , such that and , then the well-known Hardy-Hilbert's inequality and its equivalent form are given by
where the constant factors are all the best possible [1]. It attracted some attention in the recent years. Actually, inequalities (1.1) and (1.2) have many generalizations and variants. Equation (1.1) has been strengthened by Yang and others ( including integral inequalities ) [2–11].
In 2006, Yang gave an extension of [2] as follows.
If , , such that , , then
is the Beta function.
In 2007 Xie gave a new Hilbert-type Inequality [3] as follows.
If , and the right of the following inequalities converges to some positive numbers, then
The main objective of this paper is to build a new Hilbert's inequality with a best constant factor and some parameters.
In the following, we always suppose that
(1), , ,
(2)both functions and are differentiable and strict increasing in and respectively,
(3) are strictly increasing in and respectively. is strict decreasing on and ,
(4)
2. Some Lemmas
Lemma 2.1.
Define the weight coefficients as follows:
then
where
Proof.
Let then if then
if ), then
On the other hand, . Setting , then Similarly, .
Lemma 2.2.
For one has
Proof.
The lemma is proved.
Lemma 2.3.
Setting (or and (or , resp.), then is strictly decreasing, then
There for any ).
Proof.
We have
Easily, had up bounded when
3. Main Results
Theorem 3.1.
If , , , then
is defined by Lemma 2.1.
Proof.
By Hölder's inequality [12] and (2.5),
setting By(3.1) we have
By and (3.4) taking the form of strict inequality, we have (3.1). By Hölder's inequality[12], we have
as . By (3.2), (3.5) taking the form of strict inequality, we have (3.1).
Theorem 3.2.
If , then both constant factors, and of (3.1) and (3.2), are the best possible.
Proof.
We only prove that is the best possible. If the constant factor in (3.1) is not the best possible, then there exists a positive (with ), such that
For , setting , then
On the other hand and ),
By (3.6), (3.7), (3.8), and Lemma 2.3, we have
We have , . This contracts the fact that .
References
Hardy GH, Littlewood JE, Pólya G: Inequalities. Cambridge University Press, Cambridge, UK; 1952:xii+324.
Yang BC: On Hilbert's inequality with some parameters. Acta Mathematica Sinica. Chinese Series 2006,49(5):1121–1126.
Xie Z: A new Hilbert-type inequality with the kernel of --homogeneous. Journal of Jilin University. Science Edition 2007,45(3):369–373.
Xie Z, Yang B: A new Hilbert-type integral inequality with some parameters and its reverse. Kyungpook Mathematical Journal 2008,48(1):93–100.
Yang B: A Hilbert-type inequality with a mixed kernel and extensions. Journal of Sichuan Normal University. Natural Science 2008,31(3):281–284.
Xie Z, Zeng Z: A Hilbert-type integral with parameters. Journal of Xiangtan University. Natural Science 2007,29(3):24–28.
Wenjie W, Leping H, Tieling C: On an improvenment of Hardy-Hilbert's type inequality with some parameters. Journal of Xiangtan University. Natural Science 2008,30(2):12–14.
Xie Z: A new reverse Hilbert-type inequality with a best constant factor. Journal of Mathematical Analysis and Applications 2008,343(2):1154–1160. 10.1016/j.jmaa.2008.02.007
Yang B: On an extended Hardy-Hilbert's inequality and some reversed form. International Mathematical Forum 2006,1(37–40):1905–1912.
Xie Z: A Hilbert-type inequality with the kernel of irrational expression. Mathematics in Practice and Theory 2008,38(16):128–133.
Xie Z, Rong JM: A new Hilbert-type inequality with some parameters. Journal of South China Normal University. Natural Science Edition 2008,120(2):38–42.
Kang J: Applied Inequalities. Shangdong Science and Technology Press, Jinan, China; 2004.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
About this article
Cite this article
Zeng, Z., Xie, Zt. A Hilbert's Inequality with a Best Constant Factor. J Inequal Appl 2009, 820176 (2009). https://doi.org/10.1155/2009/820176
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1155/2009/820176