OA, OB are opposite rays and ∠AOC + ∠BOD= 90°

Match the items on the right to the items on the left.

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since OA and OB are opposite rays, AB is line.

since ray OC stands on line AB, ∠AOC+∠COB=180°

∠AOC+∠COD+∠BOD=180°

(∠AOC+∠BOD)+∠COD=180°

90°+ ∠COD=180°

∠COD=180°-90°=90°