\input{preamble-standalone.ltx}
\begin{document}

% Ex. No. 81 (Section 10.1.1 : Example with \tkzcname{tkzShowBB})

\begin{tikzpicture}[scale=.5]
  \tkzInit[ymax=5,xmax=8]
  \tkzGrid
  \tkzDefPoint(3,0){A}
   \begin{scope}
    \tkzClipBB
    \tkzDrawCircle[R](A,5 cm)
     \tkzShowBB
   \end{scope}
\tkzDrawCircle[R,red](A,4 cm)
\end{tikzpicture}

\end{document}