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How to write the set of rational numbers in Latex !

In old books, classic mathematical number sets are marked in bold as follows

```
$\mathbf{Q}$ is the set of rational numbers.
```

So we use the **\ mathbf** command. Which give:

$\mathbf{Q}$ is the set of rational numbers.

You will have noticed that in recent books, we use a font that is based on double bars, this notation is actually derived from the writing of classic sets on the blackboard: indeed, on the blackboard we do not fill these sets, or it would take a ton of chalk !!! In Latex, we use the **amsfonts** package

In the preamble we have:

```
\usepackage{amsfonts}
```

and **\mathbb** command

```
$\mathbb{Q}$ is the set of rational numbers.
```

$\mathbb{Q}$ is the set of rational numbers.

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