[texhax] Please help with a Mathematical Symbol

[Robin Fairbairns]

> 
>      I would like to write n choose 2 using the standard mathematical symbol
> of parenthesis and n written above 2 with nothing between them. From reading
> the documentation, I thought the following would do it:
> 
>             \begin{displaymath}
>             \binom{r}{2}
>             \end{displaymath}
> 
> However, LaTeX says that \binom is an undefined control sequence. I am using
> the MikTex version of LaTeX. Could somebody please help?

\binom is defined in the amsmath package; load that and all will be
well.