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How do I make a symbol for the length of a line or vector? I intend the following notation: |AD| is the length of AD. I can't find this symbol anywhere. (When I use shift+backslash in LaTeX, it gives a horizontal line).

For some reason the \cdot also doesn't seem to work, when I write it down like this:

&|AD| \cdot |BD|& = ...

So can anyone please tell me what I am doing wrong?

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marked as duplicate by Ludovic C., Peter Jansson, Claudio Fiandrino, Red, karlkoeller Nov 7 '13 at 15:33

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2  
Did you try putting them in math mode $\| AB \|$ and & is a special character (in geeneral) column separator for tables and arrays. –  percusse Nov 7 '13 at 14:37
    
Have a look at this question and its answers How to look up a symbol or identify a math alphabet?. –  Ludovic C. Nov 7 '13 at 14:40
1  
shift+\ to me means | (a vertical bar). Do you get an horizontal line? –  Sigur Nov 7 '13 at 14:56
    
@LudovicC. The question was not about any symbol, but about delimiters instead. In that sense it is not a duplicate of the cited answer. –  Michael Hoppe Nov 7 '13 at 16:25
    
@MichaelHoppe Sure but it turns out that Detexify provides the right commands to get this delimiter. Plus I don't see really the difference between a symbol and a delimiter (in this context). –  Ludovic C. Nov 7 '13 at 16:33

2 Answers 2

Usually you use \[ \lvert AD \rvert \cdot \lvert BD \rvert \] relying on the amsmath package for this task. Often people wrap this into a macro called \abs or \norm like this:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\norm}[1]{\lvert #1 \rvert}

\begin{document}
\[
    \norm{AD}\cdot\norm{BD}
\]
\[
    \lvert AD \rvert \cdot \lvert BD \rvert
\]
\end{document}
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You can use |, as you wish, but in the math mode: $|AD|\cdot|CD|$. The same character from a keybord gives in text mode horizontal line (em dash, in fact).

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Ow!! I've just discovered that the vertical bar in text mode produces an em dash line... lol –  Sigur Nov 7 '13 at 15:36

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