\begin{tikzpicture}[scale=1.25] \tkzInit[xmin=0,xmax=4,ymin=0,ymax=3] \tkzClip \tkzDefPoint(0,0){A} \tkzDefPoint(4,0){B} \tkzDefPoint(1,3){C} \tkzDrawPolygon(A,B,C) \tkzSetUpLine[color=magenta] \tkzDrawLine[altitude](B,C,A) \tkzDrawLine[altitude](C,A,B) \tkzDrawLine[altitude](A,B,C) \end{tikzpicture}