http://www.***.com/tools/maths/
http://baike.baidu.com/view/91555.htm
http://school.hfcas.ac.cn/Article/ShowArticle.asp?ArticleID=288
http://www.***.com/tools/maths/
http://baike.baidu.com/view/91555.htm
http://school.hfcas.ac.cn/Article/ShowArticle.asp?ArticleID=288