\input{preamble-standalone.ltx} \begin{document} % Ex. No. 230 (Section 30.1.5 : Altitudes - other construction) \begin{tikzpicture}[scale=.75] \tkzDefPoint(0,0){A} \tkzDefPoint(8,0){B} \tkzDefPoint(3.5,10){C} \tkzDefMidPoint(A,B) \tkzGetPoint{O} \tkzDefPointBy[projection=onto A--B](C) \tkzGetPoint{P} \tkzInterLC(C,A)(O,A) \tkzGetSecondPoint{M} \tkzInterLC(C,B)(O,A) \tkzGetFirstPoint{N} \tkzInterLL(B,M)(A,N) \tkzGetPoint{I} \tkzDrawCircle[diameter](A,B) \tkzDrawSegments(C,A C,B A,B B,M A,N) \tkzMarkRightAngles[fill=brown!20](A,M,B A,N,B A,P,C) \tkzDrawSegment[style=dashed,color=orange](C,P) \tkzLabelPoints(O,A,B,P) \tkzLabelPoint[left](M){$M$} \tkzLabelPoint[right](N){$N$} \tkzLabelPoint[above](C){$C$} \tkzLabelPoint[above right](I){$I$} \tkzDrawPoints[color=red](M,N,P,I) \tkzDrawPoints[color=brown](O,A,B,C) \end{tikzpicture} \end{document}