a)
m(∡ AOB)=2x+20° , m(∡ BOC)=3x+ 10° si m(∡ COA)= 4x+15°
m(∡ AOB)+ m(∡ BOC)+ m(∡ COA)= 360°
2x+20°+3x+ 10°+ 4x+15°=360°
9x+45°=360°
9x=315°
x=315°:9=35°
m(∡ AOB)=2x+20°=2*35°+20°=90°
m(∡ BOC)=3x+ 10°=3*35°+10°=115°
m(∡ COA)= 4x+15°=4*35°+15°=155°
b)
m (∡ MON)=
m (∡ COB)/2
+m (∡ COA)/2=
(115°+155°)/2=270/2=135°