o为BD中点?
若E在CD延长线上;tan∠BCD=OD/OC=AE/CE,OC≠CE,假设不成立
E在CD边上∠AED=∠AOD=90°,AE=OD,AD=AD,所以△AED≌△DOA,∠AED=∠ADO=1/2∠ADC,∠AED+∠ADC=90°,∠DAE=30°∠CAE=∠DAC-∠DAE,∠DAC=∠ADC=60°,
∠CAE=30°