**Given :** Two congruent circles with centres O and O′. AB and CD are equal chords of the circles with centres O and O′ respectively.

**To Prove :** ∠AOB = ∠COD

**Proof : **In triangles AOB and COD,

AB = CD [Given]

AO = CO '

BO = DO ' [Radii of congruent circle]

⇒ ∆AOB ≅ ∆CO′D [SSS axiom]

⇒ ∠AOB ≅ ∠CO′D **Proved.** [CPCT]