Ar trebui ca m(COB)=6x, iar in acest caz m(AOB)+m(COB)+m(AOC)=360 grade:
2x + 50 + 6x + x + 40 = 360, de unde x = 30.
Rezulta: m(AOB)=110, m(COB)=180, m(AOC)=70.
Deasemenea, m(AOM)=m(MOB)=110/2=55 si m(AON)=m(NOC)=70/2=35
Rezulta: m(MON) = 55 + 35 = 90 grade (unghi drept).