1Bottema,R Z Djcrdjevic' ,R R Janic'. Geometric Inequalities [M]. Groningen: Wolters-Noordhoff, 1969:53-54.
2D S Mitrinovic', J E peearic' ,V Volenec. Recent Advances in Geometric Inequalities [M]. Kluwer Academic Publishers, 1989:2-3.
3S. H. Wu and Z. H. Zhang, Some strengthened results on C, erretsen's inequalities. Research Group in Mathematical Inequalities and Applications[J]. 2003,6 (3):583-590.
