(1)连接OD.∵OB=OD∴∠OBD=∠ODB∵AC=BC∴∠OBD=∠A∴∠ODB=∠A∴OD//AC∴∠EDO=∠EFC=90°∴EF为切线.(2)过A作AH⊥BC.∵∠EFC=∠AHC=90°,∠ACE=∠ACE∴∠E=∠CAH∵AH²=AB²-BH²=AC²-CH²即...