\documentclass{article} % say
\usepackage{tikz}
\begin{document}
%We are working on
\begin{tikzpicture}
\usetikzlibrary{patterns}

% traits horizontaux


\node (A) at (-6,5) [coordinate] {} ;
\node [above left] at (A) {A} ;

\node (B) at (-6,1) [coordinate] {} ;
\node [below left] at (B) {B} ;

\node (C) at (0,0) [coordinate] {} ;
\node [below left] at (C) {C} ;

\node (D) at (4,1.5) [coordinate] {} ;
\node [below right] at (D) {D} ;

\node (E) at (1.5,4.5) [coordinate] {} ;
\node [above right] at (E) {E} ;

\node (a) at (1.75,2.75) [coordinate] {} ;
\node [above right] at (a) {a} ;

\node (b) at (-6,2.5) [coordinate] {} ;
\node [left] at (b) {b} ;

\node (c) at (2.2,0.825) [coordinate] {} ;
\node [below right] at (c) {c} ;

%figure de gauche
\draw (B) -- (C) -- (D) -- (E) -- (A) -- (B);
\draw (A) -- (C) -- (E);
\draw (-3,0.5) -- (-3,2.5) -- (-2.25,4.75);
\draw [dashed] (B) --  (D) -- (A);
\draw [dashed] (-3,0.5) -- (-1,1.25) -- (-1,3.25) -- (-2.25,4.75);
\draw [dashed] (-3,2.5) -- (-1,3.25);


\draw [line width=1pt,densely dashed] (A) -- (a) -- (c) -- (A);
\filldraw[color=lightgray,pattern=vertical lines] (A) -- (a) -- (c) ;

\draw [line width=1pt,densely dashed]  (A) -- (b) -- (c);
\filldraw[color=lightgray,pattern=horizontal lines] (A) -- (b) -- (c) ;
% textes

%fleches
\draw[->] (-2,-0.5) -- (-2,-1.5);
\draw (-2.8,-1) node{e};

\draw (-6,-2.5) -- (2,-2.5);
\draw (-4,-2.3) node{$\tau$};
\filldraw [black] (-2,-2.5) circle (1.5pt);
\draw (-2,-2.9) node{$y$};
\filldraw [black] (-6,-2.5) circle (1.5pt);
\filldraw [black] (2,-2.5) circle (1.5pt);

\draw [line width=1.5pt,densely dashed] (-1.91,1.675) -- (-1.89,2.875) --  (-2.125,3.875);

\end{tikzpicture}


\end{document}