% This picture represents the action of the dihedral group in the real plain
% (C) Thiago Brevidelli
\begin{tikzpicture}
  % The axis
  \draw[->] (-3,0)--(3,0) node[right]{$x$};
  \draw[->] (0,-2)--(0,2) node[above]{$y$};
   
  % The triangle
  \node[draw, regular polygon, regular polygon sides=3, minimum height=2cm]{};
  
  % The action of sigma
  \draw[->] (1.5, 0.5) arc (0:90:1cm) 
            node at (1.5, 1.4) {$\sigma$};

  % The action of tau
  \draw[<->] (-1, -1)--(1, -1) node[right]{$\tau$};
\end{tikzpicture}   

