设BD与EF相交于点M∵AD∥BC,AD⊥BD,E、F为AB、CD中点∴EF⊥BD于点M,且DM=BM,EF∥AD∥BC又①DE=BF可得△DEM≌△BFM（HR定理）∴∠DEF=∠BFE又∠ADE=∠DEF,∠CBF=∠BFE,∠AEF=∠CFE（内错角相等定理）有②∠ADE=∠CBF,...