Code:
\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[>=stealth,thick]
% \draw[help lines] (0,0) grid (5,5);
\draw[<->] (0,5) |- (5,0);
\foreach \x/\xtext in {1/1,3/2}
\draw (\x,0)--(\x,-3pt) node[below] {$x_\xtext$};
\foreach \y/\ytext in {2/1,4/2}
\draw (0,\y)--(-3pt,\y) node[left] {$y_\ytext$};
\draw (1.5,0)--(1.5,-3pt) node[below] {$x$};
\draw (0,2.5)--(-3pt,2.5) node[left] {$y$};
\draw[dotted] (0,2) -| (1,0) (0,2.5) -| (1.5,0) (0,4) -| (3,0);
\draw[red] (1,2) node[black] {\Large $\times$} -- (3,4) node[black] {\Large $\times$};
\end{tikzpicture}
\end{document}
MfG
Thorsten¹
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