ho il sospetto (ma non prove certe ) che la colpa sia di beamer
infatti togliendo nell’immagine i suoi comandi il disegno compare
`
\documentclass{beamer}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage[italian]{babel}
\usepackage{default}
\usepackage{times}
\usepackage{tikz}
\usetikzlibrary{calc}
%\usetikzlibrary{shapes,arrows,trees,positioning}
\usetikzlibrary{shapes,arrows,trees,positioning,through,intersections,fadings}
%\usetikzlibrary{shapes.gates.logic.US,shapes.gates.logic.IEC}
\usetheme{Torino}
\begin{document}
\begin{frame}[t]{scaleno, isoscele, equilatero}
\begin{center}
% % \begin{figure}
\scalebox{0.5}{
\begin{tikzpicture}
\tikzstyle{etichetta} = [draw,node distance=.5, text centered, very thick,text width=50,minimum size=10]
% %\tikzstyle{etichetta} = [draw,outer sep=0,inner sep=1,minimum size=10,node distance=1]
\tikzstyle{etichetta2} = [etichetta,node distance=55, color=red, text width=50]
\tikzstyle{etichetta3} = [etichetta,node distance=80,color=red]
\tikzstyle{etichetta4} = [etichetta,node distance=70,text width=70]
\tikzstyle{linea} = [thick]
\tikzstyle{linea2} = [thick,-triangle 90]
% \onslide<1>{
\coordinate (a) at (0,0);
\coordinate (b) at (6,0);
\coordinate (c) at (9,6);
\draw[linea] (a)–(b)–(c)–cycle;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\clip (a)++(-0.5,-0.5) rectangle($(c) + (1,1)$);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\node(A)[label=$A$] at (a) {$\bullet$};
\node(B)[label=50:$B$] at (b) {$\bullet$};
\node(C)[label=$C$] at (c) {$\bullet$};
% }
%isoscele
% \onslide<2>{
\coordinate (a) at (0,0);
\coordinate (b) at (6,0);
\node(m1) at ($(a)!0.5!(b)$) {};
\node(c1) at (m1)[circle through=(b)] {};
\node(c2) at (a)[circle through=(b)] {};
\node(c3) at (b)[circle through=(a)] {};
\coordinate (ct) at (intersection 2 of c3 and c2);
\coordinate (c) at (intersection of ct–m1 and c1);
\node(A)[label=$A$] at (a) {$\bullet$};
\node(B)[label=50:$B$] at (b) {$\bullet$};
\node(C)[label=$C$] at (c) {$\bullet$};
\draw[linea] (a)–(b)–(c) –cycle;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\clip (a)++(-0.5,-0.5) rectangle($(c) + (4,5)$);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\node(m1)at ($(a)!0.5!(c)$) {$\backslash\backslash$ };
\node(m2)at ($(c)!0.5!(b)$) {$//$ };
% }
% \onslide<3>{
%equilatero
\coordinate (a) at (0,0);
\coordinate (b) at (6,0);
\node(c1) at (a)[circle through=(b)] {};
\node(c2) at (b)[circle through=(a)] {};
\coordinate (c) at (intersection 2 of c1 and c2);
\draw[linea] (a)–(b)–(c) –cycle;
\node(A)[label=$A$] at (a) {$\bullet$};
\node(B)[label=50:$B$] at (b) {$\bullet$};
\node(C)[label=$C$] at (c) {$\bullet$};
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\clip (a)++(-0.5,-0.5) rectangle($(c) + (1,1)$);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\node(m1)at ($(a)!0.5!(c)$) {$\backslash\backslash$ };
\node(m2)at ($(c)!0.5!(b)$) {$//$ };
\node(m3)at ($(a)!0.5!(b)$) {$//$ };
% }
\end{tikzpicture}
}
\end{center}
\begin{itemize}
\item<1> Triangolo scaleno
\item<2> Triangolo isoscele
\item<3> Triangolo equilatero
\end{itemize}
\end{frame}
\end{document}
`
claudio