1. [1] P. S. Bullen, A Dictionary of Inequalities, Pitman Monographs and Surveys in Pure and Applied Mathematics 97, Addison Wesley Longman Limited, 1998.
2. [2] Z.-H. Huo, D.-W. Niu, J. Cao, and F. Qi, A generalization of Jordan’s inequality and an application, Hacet. J. Math. Stat., 40 (2011), no. 1, 53–61.
3. [3] H. Kober, Approximation by integral functions in the complex domain, Trans. Amer. Math. Soc., 56 (1944), no. 1, 7–31; Availble online at https://doi.org/10.2307/1990275.10.2307/1990275
4. [4] D. S. Mitrinović, Analytic Inequalities, In cooperation with P. M. Vasić. Die Grundlehren der mathematischen Wissenschaften, Band 165 Springer-Verlag, New York-Berlin, 1970.
5. [5] D.-W. Niu, J. Cao, and F. Qi, Generalizations of Jordan’s inequality and concerned relations, Politehn. Univ. Bucharest Sci. Bull. Ser. A Appl. Math. Phys., 72 (2010), no. 3, 85–98.