AB and AC are two equal chords of a circle. Prove that the bisector of the angle BAC passes through the centre of the circle.
Given: AB and AC are two equal chords of the circle.
Prove: Centre lies on the bisector of the BAC.
Construction: Join BC
Proof: In AOB and AOC
AB = AC (given)
BAO = CAO (given)
AO = AO (common)
AOB AOC (by SAS congruence)
BO = CO (CPCT) …(i)
and AOB = AOC (CPCT)
AOB + AOC = 180° (Linear pair)
2 AOB = 180° (APB = APC)
AOB = 90°
AO is perpendicular bisector of the chord BC and BC is the diameter as BO = CO
Hence, AO passes through the centre of the circle, and O is the centre of the circle.
Hence proved