Angles subtended by chords AC and BC at the centre O of the circle are 55o and 155o respectively. What is the measure of ∠ACB?
OA=OB=OC=radius
In △OBC
Since OB=OC
∠OBC=∠OCB
∠BOC=155
∠OBC+∠OCB+∠BOC=180
2∠OCB=180−155
∠OCB=12.5
Similarly in △OAC
2∠OCA=180−55
∠OCA=62.5
2∠OCB=180−155
∠OCB=12.5
SCB = 2∠OCB=180−155
∠OCB=12.5
OCB + 2∠OCB=180−155
∠OCB=12.5∘
OCA=12.5+62.5=75∘