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

% Ex. No. 51 (Section 11.1.3 : colinear $K=\frac{\sqrt{2}}{2}$)

\begin{tikzpicture}[vect/.style={->,
	          shorten >=3pt,>=latex'}]
 \tkzDefPoint(1,1){A}
 \tkzDefPoint(4,2){B}
 \tkzDefPoint(2,2){CU}
 \tkzDefPointWith[colinear=at C,K=sqrt(2)/2](A,B)
 \tkzGetPoint{D}
 \tkzDrawPoints[color=red](A,B,C,D)
 \tkzDrawSegments[vect](A,B C,D)
\end{tikzpicture}

\end{document}
