\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{snakes}
\usepackage{verbatim}

\tikzstyle{mybox} = [draw=red, fill=blue!20, very thick,
    rectangle, rounded corners, inner sep=10pt, inner ysep=20pt]

\begin{document}

\begin{tikzpicture}[scale=1.2]
%\begin{tikzpicture}[scale=3]

    %\draw[step=0.1, color=lightgray] (-1,-1) grid(4.5,4.5);

    %\draw[help lines] (-3,-1) grid (4,1);

    \draw [thick](-2.5,0) -- (3.5,0);
    \draw [thick, style=dotted](3.5,0) -- (4,0);
    \draw [thick, style=dotted](-3,0) -- (-2.5,0);

    \foreach \x/\xtext in {-2/x_2,0,1, 3/x_1}
      \draw[xshift=\x cm, thick] (0pt,1pt) -- (0pt,-1pt) node[below,fill=white]
            {$\xtext$};

    \draw[snake=brace, mirror snake, color=blue] (-2,-0.4) -- (0,-0.4) node[midway,sloped,below] {$|x_1|$};
    \draw[snake=brace, mirror snake, color=red] (0,-0.4) -- (3,-0.4) node[midway,sloped,below] {$|x_2|$};


 %    \foreach \x in {1,2,3}
 %      \draw (\x cm,1pt) -- (\x cm,-1pt) node[anchor=north] {$\x$};

\end{tikzpicture}
\end{document} 