How to write \ symbol in math mode in LaTeX/MathJax? [closed]

Question

How can we insert the \ symbol in math mode for LaTeX and MathJax without loading any package that is required to achieve this symbol?

I tried

\documentclass{article}
\usepackage{amsmath}

\begin{document}
$\$
\end{document}

but the program gives errors, also with ${\}$, \text{\} etc. fails. In MathJax I use $\$ and it produces error.

The context of the problem is I want to represent the (missing) \ symbol inside a formula (not in SE). The solution is add that symbol, so I want to alert the user "Hey, you forgot to add $\$ in ${1,2,3}$. It should be $\{1,2,3\}$" (of course the site does not have single quotes (`)).

Thanks!!

Answer 1

You probably want to use the backslash to exclude elements from a set. To this end use \setminus. To get the set of all integers without zero, you'd write

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
$\mathbb{Z} \setminus \{ 0 \}$
\end{document}

Also works in MathJax. Live example: http://mathb.in/29559

Answer 2

I often prefer to use \smallsetminus because the slash is lower down.

In this link http://docs.mathjax.org/en/latest/tex.html. I have seen that there is a possibility of using it with MathJax.

\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}
$\mathbb{R}\smallsetminus\{0\}$
\end{document}