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Research Article | Open Access

Volume 2013 |Article ID 578036 | https://doi.org/10.1155/2013/578036

Huo Tang, Guan-Tie Deng, "New Subclasses of Analytic Functions with Respect to Symmetric and Conjugate Points", Journal of Complex Analysis, vol. 2013, Article ID 578036, 9 pages, 2013. https://doi.org/10.1155/2013/578036

# New Subclasses of Analytic Functions with Respect to Symmetric and Conjugate Points

Accepted11 Nov 2012
Published04 Feb 2013

#### Abstract

We introduce new subclasses of close-to-convex and quasiconvex functions with respect to symmetric and conjugate points. The coefficient estimates for functions belonging to these classes are obtained.

#### 1. Introduction

Let be the class of functions which are analytic and univalent in the open unit disk given by and satisfying the conditions , , .

Let denote the class of functions which are analytic and univalent in of the form

Let be the subclass of functions and satisfying the condition These functions are called starlike with respect to symmetric points and were introduced by Sakaguchi .

Also, let be the subclass of functions and satisfying the condition These functions are called starlike with respect to conjugate points and were introduced by El-Ashwah and Thomas . Further results on starlike functions with respect to symmetric points or conjugate points can be found in .

Then, Das and Singh  introduced another class , namely, convex functions with respect to symmetric points and satisfying the condition

Suppose that and are two analytic functions in . Then, we say that the function is subordinate to the function , and we write , , if there exists a Schwarz function with and such that .

In view of subordination definition, Goel and Mehrok  introduced a subclass of denoted by .

Let be the class of functions of the form (2) and satisfying the condition

Following them, many authors introduced the analogue definitions by extension as follows (see [8, 9]).

Definition 1. Let be the subclass of consisting of functions given by (2) satisfying the condition
Let be the subclass of consisting of functions given by (2) satisfying the condition
Let be the subclass of consisting of functions given by (2) satisfying the condition

Motivated by the pervious classes, Selvaraj and Vasanthi  defined the following classes of functions with respect to symmetric and conjugate points.

Definition 2. Let be the subclass of consisting of functions given by (2) satisfying the condition
Let be the subclass of consisting of functions given by (2) satisfying the condition

In this paper, we introduce the class consisting of analytic functions of the form (2) and satisfying where .

In addition, we introduce the class consisting of analytic functions of the form (2) and satisfying where .

We note that(i)for , (see Mehrok et al. ) and ;(ii)for and , (see Janteng and Halim ) and ;(iii)for and , and ;(iv)for , and ;(v)for and , (see Janteng and Halim ) and ;(vi)for and , and .

By the definition of subordination, it follows that if and only if and that if and only if where

In the next section, we discuss the coefficient estimates for functions belonging to the classes and .

#### 2. Some Preliminary Lemmas

We will require the following lemmas for proving our main results.

Lemma 3 (see ). If is given by (14), (15) and (16), then for  ,

Lemma 4 (see ). Let . Then, for , ,

Lemma 5 (see ). Let . Then, for , ,

#### 3. Main Results

Unless otherwise mentioned, we will assume in the reminder of this paper that , , and .

Theorem 6. Let , then for ,

Proof. Since , it follows that for , with , where .
On equating the coefficients of like powers of in (22), we get and continuing in this way, we obtain From (14) and (16), we have
On equating the coefficients, we obtain and so By using Lemma 3 and (27), we have Again, by applying Lemma 3 and using (23), we obtain from (28) It follows that (20) and (21) hold for . We now prove (20) and (21) by induction.
Equation (29) together with Lemma 3 yield
Again, using Lemma 3 in (25), we have
Using (34) in (33), we obtain We suppose that (20) and (21) hold for .
Using Lemma 4 in (32) and (35), we get In order to prove (20), it is sufficient to show that Thus, (38) is valid for .
Let us assume that (38) is true for all . Then, from (36), we have Thus, (38) holds for , and, hence, (20) follows. Next, we prove (21).
From (38), we have
By using (40) in (37), we obtain which proves (21).

By taking and in Theorem 6, respectively, we can readily deduce the following corollaries.

Corollary 7 (see ). Let , then, for ,

Corollary 8. Let , then, for , Further, putting and in Corollary 8, one obtains the following.

Corollary 9. Let , then, for ,

Remark 10. Corollary 9 improves the result obtained by Janteng and Halim [13, Theorem 3.1].

Theorem 11. Let , then, for ,

Proof. Since it follows that where .
On equating the coefficients of like powers of in (47), we get and continuing in this way, we obtain From (15) and (16), we have
On equating the coefficients, we obtain and so By using Lemma 3, (48), and (54), we have Again, by applying Lemma 3 and using (48)–(50), we obtain from (55) and (56) It follows that (45) and (46) hold for . We now prove (45) by induction.
Equation (57) together with Lemma 3 yield Again, by using Lemma 3 in (51), we have Using (62) in (61), we obtain We suppose that (45) holds for .
Using Lemma 5 in (63), we get In order to prove (45), it is sufficient to show that Thus, (65) is valid for .
Let us assume that (65) is true for all , . Then, from (64), we have Thus, (65) holds for , and, hence, (45) follows. Similarly, we can prove (46).

By taking and in Theorem 11, respectively, we can easily derive the following corollaries.

Corollary 12. Let , then, for ,

Corollary 13. Let , then, for ,

#### Acknowledgments

The present investigation was partly supported by the Natural Science Foundation of China under Grant no. 11271045, the Higher School Doctoral Foundation of China under Grant no. 20100003110004, and the Natural Science Foundation of Inner Mongolia of China under Grant no. 2010MS0117. The authors would like to thank Professor Jacek Dziok for his valuable suggestions and the referees for their careful reading and helpful comments to improve the paper.

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