Given:
AB =AC
AB and AC lies on the opposite sides of OA
The chords of equal length, are equidistant from the centre of the circle.
In ∆OAB and ∆OAC,
AB = AC (given)
OA = OA (common)
OB = OC (radius of the circle)
By SSS property,
∆OAB ≅ ∆OAC
Therefore, ∠OAB = ∠OAC (by C.P.C.T.)
Hence, ∠OAB = ∠OAC.