1. Department of Mathematics, Education Faculty, Anadolu University, Eskisehir, Turkey;
2. Department of Mathematics, Faculty of Sciences, Gazi University, Ankara, Turkey;
3. Department of Mathematics, The University of Danang - University of Science and Education, Danang City, Vietnam;
4. Faculty of Mathematics, Vinh University, Vinh City, Nghe An Province, Vietnam;
5. Department of Business Administration, Faculty of Economics and Administrative Sciences, Balkan Campus, Edirne, Turkey