Math

http://community.wikidot.com/forum/t-81749/latex-cannot-use-underbrace

[[$ \underbrace{ a+b+\cdots+z }_{26} $]]

$\underbrace{ a+b+\cdots+z }_{26}$

http://community.wikidot.com/forum/t-181519/latex:sum-translates-in-a-wrong-way

If $\sum$ is placed in a fraction, it'll be typeset in text style unless you tell LATEX otherwise:

What you type …	What you get …
[[math]] \sqrt{6 \over \sum^6_{x=6}{7x}} [[/math]]	(1) \begin{align} \sqrt{6 \over \sum^6_{x=6}{7x}} \end{align}
[[math]] \sqrt{6 \over \displaystyle{\sum^6_{x=6}{7x}}} [[/math]]	(2) \begin{align} \sqrt{6 \over \displaystyle{\sum^6_{x=6}{7x}}} \end{align}