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Question
In the following figure, O is the centre of the circle, ∠AOB = 60° and ∠BDC = 100°. Find ∠OBC.
Solution
Here, `∠ACB = 1/2 ∠AOB`
= `1/2 xx 60^circ`
= 30°
(Angle at the centre is double the angle at the circumference subtended by the same chord)
By angle sum property of ΔBDC,
∴ ∠DBC = 180° – 100° – 30° = 50°
Hence, ∠OBC = 50°
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