In a circle with centre O, quadrilateral ABCD is inscribed. It is given that ∠AOB=∠COD and ∠BOC=70∘.
a. (i) Prove that AB=CD.
b. (ii) If ∠AOB=110∘, find the value of ∠ADC.
c. (iii) If the length of AB is 8.4cm, determine the length of CD with justification.