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## Nonlinear Problems: Analytical and Computational Approach with Applications

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Research Article | Open Access

Volume 2012 |Article ID 391038 | https://doi.org/10.1155/2012/391038

Qing Yang, Jin-Lin Liu, "Argument Property for Certain Analytic Functions", Abstract and Applied Analysis, vol. 2012, Article ID 391038, 8 pages, 2012. https://doi.org/10.1155/2012/391038

# Argument Property for Certain Analytic Functions

Accepted01 Nov 2011
Published11 Dec 2011

#### Abstract

Let P be the class of functions p(z) of the form which are analytic in the open unit disk . The object of the present paper is to derive certain argument inequalities of analytic functions p(z) in P.

#### 1. Introduction

Let be the class of functions of the form which are analytic in the open unit disk . For functions and in the class , we say that is subordinate to if there exists an analytic function in with , , and such that . We denote this subordination by If is univalent in , then this subordination is equivalent to and .

Recently, several authors investigated various argument properties of analytic functions (see, e.g., [16]). The object of the present paper is to discuss some argument inequalities for in the class .

Throughout this paper, we let

In order to prove our main result, we well need the following lemma.

Lemma 1.1 (see [6]). Let and . Also let If satisfies where is (close to convex) univalent, then The bounds and in (1.7) are sharp for the function defined by

Remark 1.2 (see [6]). The function defined by (1.8) is analytic and univalently convex in and

#### 2. Main Result

Our main theorem is given by the following.

Theorem 2.1. Let If satisfies where where denotes , then The bounds and in (2.2) are the largest numbers such that (2.4) holds true.

Proof. By taking in Lemma 1.1, we find that if satisfies where then (2.4) holds true.
For , and , we get
We consider the following two cases.
(i) If then from (2.7), and (2.6), we have and so where ,, , ,
We now calculate the maximum value of . It is easy to verify that and that
Set then . Noting that we easily have Hence, , and it follows from (2.11) to (2.16) that where denotes . Thus, by using (2.1), (2.10), and (2.17), we arrive at
(ii) If , then we obtain which leads to where ,, , ,
Now, we have Let then , , Hence, we deduce that and where . Further, by using (2.1), (2.20), and (2.25), we find that In view of , we conclude from (2.18) and (2.26) that properly contains the angular region in the complex -plane. Therefore, if satisfies (2.2), then the subordination relation (2.5) holds true, and thus we arrive at (2.4).
Furthermore, for the function defined by (1.8), we have Hence, by using (2.18) and (2.25), we see that the bounds and in (2.2) are best possible.

#### Acknowledgment

The authors would like to express sincere thanks to the referees for careful reading and suggestions which helped them to improve the paper.

#### References

1. J.-L. Liu, “The Noor integral and strongly starlike functions,” Journal of Mathematical Analysis and Applications, vol. 261, no. 2, pp. 441–447, 2001.
2. M. Nunokawa, “On the order of strongly starlikeness of strongly convex functions,” Proceedings of Japan Academy. Series A, vol. 69, no. 7, pp. 234–237, 1993.
3. M. Nunokawa, S. Owa, E. Y. Duman, and M. Aydoğan, “Some properties of analytic functions relating to the Miller and Mocanu result,” Computers & Mathematics with Applications, vol. 61, no. 5, pp. 1291–1295, 2011.
4. N. Takahashi and M. Nunokawa, “A certain connection between starlike and convex functions,” Applied Mathematics Letters, vol. 16, no. 5, pp. 653–655, 2003.
5. N. Xu, D.-G. Yang, and S. Owa, “On strongly starlike multivalent functions of order β and type α,” Mathematische Nachrichten, vol. 283, no. 8, pp. 1207–1218, 2010.
6. D.-G. Yang and J.-L. Liu, “Argument inequalities for certain analytic functions,” Mathematical and Computer Modelling, vol. 52, no. 9-10, pp. 1812–1821, 2010.

Copyright © 2012 Qing Yang and Jin-Lin Liu. 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.
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