# Error while displaying bold R \mathbb [duplicate]

Here's my sample code :

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}
\begin{document}
\pagenumbering{roman}
\section*{Problem 1}
Given that : \\
$$x \epsilon \mathbb{R} (3,2)$$
\end{document}


I get the following compilation error when using overleaf :

Undefined control sequence.
l.19 $$x \epsilon \mathbb {R} (3,2)$$


How could I fix this ?

• you need to load amssymb or amsfonts Jan 31 '16 at 22:29
• Also, $$...$$ is deprecated in LaTeX Jan 31 '16 at 22:31
• @Au101 : what should I use in place of $$...$$ then ? Jan 31 '16 at 22:38
• $...$ follow the hyperlink (click on "deprecated" in my comment) to read more. Also, you shouldn't have the \\, just get rid of it and let $...$ handle the skip. Unless you want to start a new paragraph (you probably don't), in which case, leave a blank line Jan 31 '16 at 22:40
• Do this very rarely. Start new paragraphs by leaving a complete blank line. \\  has many legitimate uses, such as in tables, and it does force a line break, but it does not end a paragraph and is rarely needed in the main text. Of course, sometimes you might want it, and in that case, go ahead. It's often used in the verse environment for typesetting poetry, for instance. tex.stackexchange.com/questions/82664/when-to-use-par-and-when, also: tex.stackexchange.com/questions/136942/… Jan 31 '16 at 22:50