Question

跪求学霸解答 几何题 谢谢

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Answer 1

追答

证明:过A做AE⊥BC，过D做DF⊥BC
∵AB = AC，∠BAC=90°
∴2AE=BC
∵AD//BC
∴AE = DF
∵DB = CB
∴2DF = BD
∵DF⊥BC
∴∠DBC = 30°
∴∠BDC = ∠BCD = 75°
∵AB = AC，∠BAC = 90°
∴∠ACB = 45°
∴∠ACD =75°-45°=30°
∴∠DOC = 75°
∴∠COD = ∠CDO
∴CO=CD

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