::
Una versione migliore:
`\begin{tikzpicture}
\draw [help lines] (-2,-1) grid (2,2);
\draw [fill=cyan!20] (0,0) circle (1);
\draw ({-sqrt(3)}, -1) node [below left] {$c_1$}
— ({sqrt(3)}, -1) node [below right] {$c_2$}
— (0, 2) node [above] {$c_3$}
— cycle;
\end{tikzpicture}`
