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

% Ex. No. 161 (Section 20.2.2 : More complex example of a line-circle intersection)

\begin{tikzpicture}[scale=.75]
  \tkzDefPoint(0,0){A}
  \tkzDefPoint(8,0){B}
  \tkzDefMidPoint(A,B)
  \tkzGetPoint{O}
  \tkzDrawCircle(O,B)
  \tkzDefMidPoint(O,B)
  \tkzGetPoint{O'}
  \tkzDrawCircle(O',B)
  \tkzDefTangent[from=A](O',B)
  \tkzGetSecondPoint{E}
  \tkzInterLC(A,E)(O,B)
  \tkzGetSecondPoint{D}
  \tkzDefPointBy[projection=onto A--B](D)
   \tkzGetPoint{F}
  \tkzMarkRightAngle(D,F,B)
  \tkzDrawSegments(A,D A,B D,F)
  \tkzDrawSegments[color=red,line width=1pt,
      opacity=.4](A,O F,B)
  \tkzDrawPoints(A,B,O,O',E,D)
  \tkzLabelPoints(A,B,O,O',E,D)
\end{tikzpicture}

\end{document}