D. S. Mitrinovic and D. D. Adamovic, Sur une inegalite elementaire ou interviennent des fonc-tions trigonometriques, Univ u Beogradu. Publik. Elektr. Fakulteta. S. Matematika i Fizika, vol.149, p.2334, 1965.

D. S. Mitrinovic, Analytic inequalities, 1970.

J. Sandor and M. Bencze, On Huygens' trigonometric inequality, vol.8, p.14, 2005.

C. Chen and J. Sandor, Inequality chains for Wilker, Huygens and Lazarevic type inequalities, J. Math. Inequal, vol.8, issue.1, p.5567, 2014.

E. Neuman, Renements and generalizations of certain inequalities involving trigonometric and hyperbolic functions, Adv. Inequal. Appl, vol.1, issue.1, pp.1-11, 2012.

Z. Yang, Three families of two-parameter means constructed by trigonometric functions, J. Inequal. Appl, p.2013, 2013.

J. S. Sumner, A. A. Jagers, M. Vowe, and J. Anglesio, Inequalities involving trigonometric functions, Amer. Math. Monthly, vol.98, pp.264-267, 1991.

C. Chen and W. Cheung, Sharpness of Wilker and Huygens type inequalities, J. Inequal. Appl, vol.2012, p.72, 2012.