# tikz: drawing arrow

How can I make the left vertical lign arrow-style as the right one?

\documentclass[tikz,border=3.14mm]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[->] (0,3) -- (0,0)
node[below] {$0$} -- (3,0) node[midway,below] {$x_A$}
node[below] {$1$} -- (3,3);
\draw[red,thick] (0,1) -- (3,2);
\path (1,0.5) node {liquido} (2,2.5) node {vapore};
\end{tikzpicture}
\end{document}


You draw the whole axis system in one path. -> only adds an arrow tip at one end of the path. Therefore you need <-> to have two arrows tip at two ends.

\documentclass[tikz,border=1]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[<->] (0,3) -- (0,0)
node[below] {$0$} -- (3,0) node[midway,below] {$x_A$}
node[below] {$1$} -- (3,3);
\draw[red,thick] (0,1) -- (3,2);
\path (1,0.5) node {liquido} (2,2.5) node {vapore};
\end{tikzpicture}
\end{document}