Let BQ and CP be the bisectors of ∠ABC and ∠ACB respectively, intersecting in the interior of △ABC at R.
Let BQ intersect side AC in Q and CP intersect side AB in P.
∴ By angle bisector theorem,
Since, R lies on BQ, point R is equidistant from AB and BC.
Similarly, R lies on CP and is equidistant from AC and BC.
So, O is equidistant from BC and AC.
Therefore, point O is equidistant from all three sides AB,BC and CA of △ABC.