\documentclass[a5paper]{article}
\usepackage[margin=5mm]{geometry}
\usepackage{tikz2d-fr}
\begin{document}
\begin{tikzpicture}
\DefinirPoints[Couleur=violet,DecalLabel=0pt]{A/0,0/b B/4,0/b C/3,2/h}
\TracerSegments[Suite,Cycle,Couleurs=red,Join=bevel]{A B C}
\end{tikzpicture}
\begin{tikzpicture}
\DefinirPoints[DecalLabel=1pt]{A/0,0/bg B/4,0/bd C/3,2/h}
\TracerSegments[Suite,Cycle,Couleurs={red,blue,green}]<thick,mainlevee>{A B C}
\MarquerPoints[StyleMarque=x]{A}\MarquerPoints[StyleMarque=+]{B}\MarquerPoints{C}
\end{tikzpicture}
\begin{tikzpicture}
\DefinirPoints*{A_1/0:2/ A_2/45:2/ A_3/90:2/ A_4/135:2/ A_5/180:2/ A_6/225:2/ A_7/270:2/ A_8/315:2/}
\TracerSegments[Suite,Cycle,Couleurs={red,blue,green,yellow,orange,pink,gray,violet}]<thick,mainlevee=1cm et 1mm>{A_1 A_2 A_3 A_4 A_5 A_6 A_7 A_8}
\TracerSegments[]<semithick,densely dotted,mainlevee>{A_1/A_5 A_2/A_6 A_3/A_7 A_4/A_8}
\end{tikzpicture}
\begin{tikzpicture}
\draw[thin,lightgray] (-5,-2) grid (8,5) ;
\DefinirPoints[Math,TaillePolice=\LARGE]{A/0,0/ B/4,1/ C/3,2/}
\ImagesPoints[TaillePolice=\tiny]{D=C+t(A>B) § E=A+t(C>B) § F=A+t(2,B>C) § G=F+t(B>D) § K=G+r(F,90) § L=B+s(C)}
\ImagePoint[Math,TaillePolice=\scriptsize]{H_1=A+t(-0.5,B>A)}
\MarquerPoints{A,B,C,D,E,F,G,K,L}
\MarquerPoint{H_1}
\end{tikzpicture}
\end{document}