Consider a quadrilateral ABCD.
(i) State the relation between the angles subtended by the same chord at two different points on the circumference of a circle.
(ii) If it is given that ∠BAD=∠BCD, explain why the four points A,B,C and D must lie on a single circle.
(iii) Once it is known that ABCD is cyclic, what conclusion can be drawn about the sum of ∠ABC and ∠ADC? Give reason.