Journal of Inequalities and Applications 
Volume 2007 (2007), Article ID 74328, 8 pages
doi:10.1155/2007/74328
Research Article

On the Strengthened Jordan's Inequality

Jian-Lin Li and Yan-Ling Li

 College of Mathematics and Information Science, Shaanxi Normal University, Xi'an 710062, China
Received 21 July 2007; Revised 19 October 2007; Accepted 22 November 2007

Recommended by Lars-Erik Persson

Abstract

The main purpose of this paper is to present two methods of sharpening Jordan's inequality. The first method shows that one can obtain new strengthened Jordan's inequalities from old ones. The other method shows that one can sharpen Jordan's inequality by choosing proper functions in the monotone form of L'Hopital's rule. Finally, we improve a related inequality proposed early by Redheffer.