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
在梯形ABCD中,AD//BC 角BAC=90度,BD=BC BD交AC于O,AB=AC 求证：CO=CD
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