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

% Ex. No. 211 (Section 25.4.1 : Example)

\begin{tikzpicture}[scale=.5]
 \tkzDefPoint(0,0){A}
 \tkzDefPoint(3,-4){B}
 \tkzDefCircle[through](A,B)
 \tkzGetLength{rABpt}
 \tkzpttocm(\rABpt){rABcm}
 \tkzDrawCircle(A,B)
 \tkzDrawPoints(A,B)
 \tkzLabelPoints(A,B)
 \tkzDrawSegment[dashed](A,B)
 \tkzLabelSegment(A,B){$\pgfmathprintnumber{\rABcm}$}
\end{tikzpicture}

\end{document}