code for diagram

> AA:=[-1,-1]:BB:=[0,0]:CC:=[5,-2]:DD:=[6,-2.4]:
tri:=plot({[AA,BB],[BB,1.2*CC]},style=line,
thickness=2,color=blue):
angl:=fsolve(-3=sqrt(2)*sqrt(29)*cos(t),t):
dtline:=plot([AA,CC],linestyle=3,thickness=3):
C1:=circarrow(BB,.5*AA, angl,4,` `,[0,0],16,blue):
dsk1:=plottools[disk](CC,.07,color=black,style=patch):
dsk2:=plottools[disk](AA,.07,color=black,style=patch):
dsk3:=plottools[disk](BB,.07,color=black,style=patch):
dsk4:=plottools[disk](DD,.07,color=black,style=patch):
txt:=plots[textplot]({[0,.3,`B`],[-1.3,-1,`A`],
[5,-2.3,`C`],[6,-2.7,`D`],[-.8,-.4,`c`],[3,-.7,`a`],
[1.5,-1.6,`b`]},
font=[TIMES,BOLD,16]):
Arr:=plottools[arrow](1.2*CC+[0, .2],CC+[0,
.2],.1,.2,.2,color=green):
plots[display]({tri,dsk1,dsk2,dsk3,dsk4,C1,txt,dtline,Arr},
axes=none,scaling=constrained);

>