per la grafica ho usato questo doc
`
\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{shapes,calc,arrows,trees,positioning,through,intersections,fadings}
\begin{document}
\begin{tikzpicture}
\coordinate (a) at (0,0);
\coordinate (b) at (6,0);
\coordinate (c) at (9,6);
\draw (a)–(b);
\draw(a)–(c);
\draw (c)–(b);
\node(A)[label=$A$] at (a) {$\bullet$};
\node(B)[label=50:$B$] at (b) {$\bullet$};
\node(C)[label=$C$] at (c) {$\bullet$};
\node(c7) at (c)[draw,circle through=(b)] {};
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\coordinate (ac) at (intersection 2 of c7 and a–c);
\node(Ca)[label=$aaaaa$] at (ac) {$\bullet$};
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{tikzpicture}
\end{document}
`
l’errore è nella prima riga penso la seconda è solo di verifica
grazie per il vostro tempo
claudio