
\begin{tikzpicture}[scale=1]
%     \foreach \i [count=\ii from 1] in {378,234,90,306,162}
% \path (\i:32mm) node (p\ii) {$X_{\ii}$};
\def\firstcircle{(1,2.5) circle (0.6cm)}
\def\secondcircle{(2.8,3.2) circle (0.6cm)}
\def\thirdcircle{(2.5,1.7) circle (0.6cm)}
 \draw \firstcircle node[] {$A$};
    \draw \secondcircle node [] {$B$};
    \draw \thirdcircle node [] {$C$};
    
    \draw (0,1) rectangle (4,4);
        \draw node at (0.3,3.8) {\small $\Omega$};
\end{tikzpicture}

