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Question
AB is the diameter of the circle with centre O. OD is parallel to BC and ∠ AOD = 60° ; calculate the numerical values of: ∠ DBC
Solution
∠BDA = 90° (Angle in a semicircle)
Also, ∠OAD is equilateral (∴ ∠OAD = 60° )
∴ ∠ODB = 90° - ∠ODA = 90° - 60° = 30°
Also, OD || BC
∴ ∠DBC = ∠ODB = 30° (Alternate angles)
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