If the two chords in a circle are equal, then the angles they subtend at the centre are the same.
Let us consider two chords AB and PQ which are of equal length.
Now, let us join the ends of the chords to the Centre of the circle.
In ΔAOB and ΔPOQ,
OA = OP = r , where r is the radius of the circle .
Also,
OB = OQ = r , and
AB = PQ (given).
∴ΔAOB≅ΔPOQ by SSS criterion.
Therefore, by C.P.C.T., ∠AOB=∠POQ.
Therefore, equal chords subtend equal angles at the centre of the circle.