In the figure, AB is common chord of the two circle. If AC and AD are diameters; prove that D,
B and C are in a straight line. O1 and O2 are the centres of two circles.
∠DBA = 90° and ∠CBA = 90°
(Angles in a semicircle is a right angle) Adding both we get,
∠DBC = 180°
∴ D, B and C form a straight line.