\input{preamble-standalone.ltx} \begin{document} % Ex. No. 87 (Section 12.2.4 : Drawing a tangent option \tkzimp{from with R} and \tkzimp{at}) \begin{tikzpicture}[scale=.5] \tkzDefPoint(0,0){O} \tkzDefRandPointOn[circle=center O radius 4cm] \tkzGetPoint{A} \tkzDefTangent[at=A](O) \tkzGetPoint{h} \tkzDrawSegments(O,A) \tkzDrawCircle(O,A) \tkzDrawLine[add = 1 and 1](A,h) \tkzMarkRightAngle[fill=red!30](O,A,h) \end{tikzpicture} \end{document}