Research Article | Open Access

# Inequality of Ostrowski Type for Mappings with Bounded Fourth Order Partial Derivatives

**Academic Editor:**Patricia J. Y. Wong

#### Abstract

A general Ostrowski’s type inequality for double integrals is given. We utilize function whose partial derivative of order four exists and is bounded.

#### 1. Introduction

In 1938, Ostrowski [1] introduced the following integral inequality.

Theorem 1. *Let : be continuous mapping on and differentiable on , whose derivative is bounded on , i.e., , then for all **The constant * is sharp in the sense that it cannot be replaced by a smaller one.

In 1975, Milovanović [2] proposed the following generalization of (1) for a function of several variables whose first order partial derivatives are bounded.

Theorem 2. *Let : be a differentiable function defined on and let in . Then, for every ,*

In 1998, Barnett and Dragomir [3] proved the following Ostrowski type inequality for mappings of two variables with bounded second order partial derivatives.

Theorem 3. *Let : continuous on , exists on and is bounded, i.e., **Then we have the inequalityfor all .*

In [4], Xue et al. derive the following inequality of Ostrowski type.

Theorem 4. *Let : be an absolutely continuous function such that the partial derivatives of order two exist and suppose that there exist constants with for all . Then we have**for all and .*

More recently, Sarikaya et al. [5] establish weighted Ostrowski type inequalities considering function whose second order partial derivatives are bounded as follows.

Theorem 5. *Let : be an absolutely continuous function such that the partial derivatives of order two exist and are bounded, i.e., **for all .Then we have**where *

For other related work, we refer the reader to [6–15].

In this paper, motivated by the ideas in both [4, 5], we shall derive a new inequality of Ostrowski’s type similar to the inequalities (5) and (7), involving functions of two independent variables.

#### 2. Main Results

In order to introduce our main results, we commence with the following lemma.

Lemma 6. *Let : be an absolutely continuous function such that the partial derivative of order 4 exists for all and . Then for any two mappings and , whereandthe identity **holds.*

*Proof. *By definitions of and in both (9) and (10), we haveFor , integration by parts yieldsSimilarly, , , and can be obtained.

Thus, by adding , , , and , we easily deduceBy further algebraic manipulations and assuming result by [4], the proof of Lemma 6 is completed.

Theorem 7. *Let : such that be an absolutely continuous function such that the partial derivative of order 4 exists and is bounded; i.e., for all . Then for all and , we havewhere the functional is given by (11).*

*Proof. *By considering (11), we haveBut,andNow, substituting (18), (19) into (17) gives (16) and, hence, completes the proof.

Corollary 8. *Under the assumption of Theorem 7 with , we have*

Corollary 9. *Under the assumption of Theorem 7 with , , and we have*

Corollary 10. *Under the assumption of Theorem 7 with , , and we have*

*Remark 11. *In Corollaries 8, 9, and 10 we assume that the involved integrals can more easily be computed than the original double integral.

#### Data Availability

No data were used to support this study.

#### Conflicts of Interest

The author declares no conflicts of interest.

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#### Copyright

Copyright © 2019 Waseem Ghazi Alshanti. 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.