In the given figure, O is the point of intersection of two chords AB and CD such that OB = OD and AOC = 45°. Then, OAC and ΔODB are


In Δ DOB and Δ AOC,
DOB = AOC = 45° (vertically opposite angle)
OAC = ODB (angles in the same segment)


OCA = OBD (angles in the same segment)
Therefore, Δ DOB Δ AOC by AA similarity,

Therefore, OC = OA.

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