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My latex file does not accept the command \backsim. This is what I wrote in the file:

$ \backsim 2.5 \mu$

What is wrong?

Przemysław Scherwentke
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Naema
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  • Are you loading amssymb package? \usepackage{amssymb} – Sigur Jun 24 '14 at 17:01
  • do you mean I need to get a package?. Lately, i loaded some packages from CTAN which seemed to be missing. Why I need to load every time?. I might have other errors and need to load more packages and my file will be full of stuff!!! – Naema Jun 24 '14 at 17:05
  • @Naema It means you should call it inside your file: \documentclass{article} \usepackage{amssymb} \begin{document} $ \backsim 2.5 \mu$ \end{document} – Przemysław Scherwentke Jun 24 '14 at 17:07
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    Just insert \usepackage{amssymb} on preamble (before \begin{document}). If you already have some AMS packages you can use comma and insert amssymb together. Usually I always load \usepackage{amsthm,amsmath,amssymb}. – Sigur Jun 24 '14 at 17:08
  • oh, I did and it solved my problem. I put \usepackage{amssymb}.thanks – Naema Jun 24 '14 at 17:48
  • @Naema: Next time you get such an error for a symbol, you can search the symbol on my page, click on it and take a look at "package" and "mode". – Martin Thoma Jun 24 '14 at 18:54
  • @Naema: Just out of curiosity: Why do you need backsim? – Martin Thoma Jun 24 '14 at 18:55
  • moose, I needed to use the mathematical symbol for approximation. I wanted to mention that a value is almost equal to 2.5um but not exactly equal. – Naema Jun 24 '14 at 22:48
  • @Naema - installing a package only makes it available. You have to specify in the document that you actually want to use it. Packages can change the way LaTeX works, so LaTeX doesn't make any assumptions about what packages you want -- you have to tell it explicitly. (Imagine trying to figure out what's going on if it didn't work that way!) – Tom Zych Jun 25 '14 at 11:02
  • yes Tom,thanks, now I understand how to fix such errors.I already put this:\usepackage{amssymb} at the begining , and my problem was solved. – Naema Jun 25 '14 at 15:53

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