a)notam x-masura <AOB
notam y-masura <BOC
x+y=180°
x=2y
=>2y+y=180°
=>3y=180°
=>y=60°
=>x=2•60°=120°
m<AOB=120°,m<BOC=60°
b)fie [OM-bisectoarea <AOB
fie [ON-bisectoarea <BOC
m<MON=?
m<MON=m<MOB+m<BON
m<AOB=120° (1)
[OM-bisect. <AOB=>m<AOM=m<MOB (2)
Din (1) si (2)=>m<MOB=120°:2=60°
m<BOC=60° (1)
[ON-bisect. <BOC=>m<BON=m<NOC (2)
Din (1) si (2)=>m<BON=60°:2=30°
=>m<MON=60°+30°=90°
