brackets

phonetic tag

http://jingyan.baidu.com/article/9f7e7ec05fe9d66f2815541a.html

http://h.hiphotos.baidu.com/exp/w=480/sign=c3aaa44f1ad8bc3ec60807c2b28ba6c8/d31b0ef41bd5ad6e72ef759f82cb39dbb6fd3cb4.jpg

binomial

\usepackage{amsmath} \binom2n