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

% Ex. No. 173 (Section 21.1.1 : Example with \tkzname{size})

\begin{tikzpicture}
   \tkzInit
   \tkzDefPoints{0/0/O,2.5/0/A,1.5/2/B}
   \tkzFillAngle[size=2cm, fill=gray!10](A,O,B)
   \tkzDrawLines(O,A O,B)
   \tkzDrawPoints(O,A,B)
\end{tikzpicture}

\end{document}