http://www.artofproblemsolving.com/wiki/index.php/LaTeX:Math
http://crab.rutgers.edu/~karel/latex/class4/class4.html
ftp://ftp.ams.org/pub/tex/doc/amsmath/short-math-guide.pdf
https://en.wikibooks.org/wiki/LaTeX/Mathematics
原文：http://www.cnblogs.com/sumile123/p/4808362.html