Journal of Inequalities and Applications
Volume 2007 (2007), Article ID 74328, 8 pages
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

Academic Editor: Lars-Erik Persson

Copyright © 2007 Jian-Lin Li and Yan-Ling Li. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.