Question

Recall that two circles are congruent if they have the same radii. Prove that equal chords of congruent circles subtend equal angles at their centres.​

Answer 1

Let us consider a circle with center O and two equal chords of a circle AB and CD.

We need to prove that ∠AOB=∠COD

In △ AOB and COD, we have

AO=CO (Radius of the circle)

BO=DO (Radius of the circle)

AB=CD (Equal chords)

By SAS criterion of congruence, we have

△AOB≅△COD

⇒∠AOB=∠COD