Solution :- Given: Two circles are drawn on sides AB and AC of a △ABC as diameters. The circles intersects at D. To prove: D lies on BC Construction: Join A and D Proof: ∠ADB = 90° (Angle in the semi-circle) ...(i) and ∠ADC = 90° (Angle in the semi-circle) ...(ii) Adding (i) and (ii), we get ∠ADB + ∠ADC = 90° + 90° => ∠ADB + ∠ADC = 180° => BDC is a straight line. Hence, D lies On third side BC.