File:Angle centre dem.svg

defaultscale := 18pt/fontsize defaultfont;

s = 13cm;

def draw_angle(expr A,O,B,r,w,col) =
    draw (O + r*unitvector(A-O))
         { r*unitvector(A-O) rotated 90 }
         ..
         { r*unitvector(B-O) rotated 90 }
         (O + r*unitvector(B-O)) withpen pencircle scaled w withcolor col;
enddef;

pair O,A,M,D,C; % C is anti-A
path p;

for i=0 upto 2:
  O := (i*s,0);
  A := (i*s,5cm);
  M := (i*s-4.924cm,-0.8682cm);
  D := (i*s+4.924cm,0.8682cm);
  C := (i*s,-5cm);
  p := A..D..C..M..cycle;
  draw p withpen pencircle scaled 1pt;
  draw M--D dashed evenly withpen pencircle scaled 1pt;
  draw O--A withcolor blue withpen pencircle scaled 1pt;
  draw_angle(D,O,A,0.8cm,1pt,blue);
  draw A--M withcolor red withpen pencircle scaled 1pt;
  draw_angle(D,M,A,0.8cm,1pt,red);
  
  label.top("A", A);
  label.bot("O", O);
  label.rt("D", D);
  label.lft("M", M);
endfor;

pair B;

B := (3.8302cm+2*s,3.2139cm);
label.urt("B", B);
draw O--B withcolor blue withpen pencircle scaled 1pt;
draw_angle(D,O,B,1.2cm,1pt,blue);
draw M--B withcolor red withpen pencircle scaled 1pt;
draw_angle(D,M,B,1.2cm,1pt,red);

D := D-(s,0);
O := O-(s,0);
M := M-(s,0);
B := (4.6985cm+s,-1.7101cm);
label.lrt("B", B);
draw O--B withcolor blue withpen pencircle scaled 1pt;
draw_angle(B,O,D,1.2cm,1pt,blue);
draw M--B withcolor red withpen pencircle scaled 1pt;
draw_angle(B,M,D,1.2cm,1pt,red);