If A, B, C are three points on a circle with centre O such that ∠AOB=90° and ∠BOC=120°, then ∠ABC=
∠BOC = 120°
∠AOC = ∠AOB + ∠BOC
= 90o + 120o
= 210°
Now,
∠ABC = 
* (Reflex ∠AOC)
= 
(360o – 210o)
= 75°
20
If A, B, C are three points on a circle with centre O such that ∠AOB=90° and ∠BOC=120°, then ∠ABC=
∠BOC = 120°
∠AOC = ∠AOB + ∠BOC
= 90o + 120o
= 210°
Now,
∠ABC = * (Reflex ∠AOC)
= (360o – 210o)
= 75°