\input{preamble-standalone.ltx} \begin{document} % Ex. No. 84 (Section 12.2.1 : Example of a tangent passing through a point on the circle ) \begin{tikzpicture}[scale=.75] \tkzDefPoint(0,0){O} \tkzDefPoint(6,6){E} \tkzDefRandPointOn[circle=center O radius 3cm] \tkzGetPoint{A} \tkzDrawSegment(O,A) \tkzDrawCircle(O,A) \tkzDefTangent[at=A](O) \tkzGetPoint{h} \tkzDrawLine[add = 4 and 3](A,h) \tkzMarkRightAngle[fill=red!30](O,A,h) \end{tikzpicture} \end{document}