Given: ∠OBD = 500
Here, AB and CD are the diameters of the circles with centre O.
∠DBC = 900 ….(i) (Angle in the semi-circle)
Also, ∠DBC = 500 + ∠OBC
900 = 500 + ∠OBC
∠OBC = 400
Again, By degree measure theorem: ∠AOC = 2 ∠ABC
∠AOC = 2∠OBC = 2 x 400 = 800