OE⊥AB,OF⊥AC,OE=OF,〈A=90度,四边形AEOF是正方形,〈EOF=90度,OE=OD=OF,△EOD和△FOD都是等腰三角形,〈OED=〈EDO,〈FDO=〈OFD,〈AOE=〈OED+〈ODE=2〈ODE,（外角等于不相邻二内角和）〈FOA=〈ODF+〈OFD=2〈FDO,（同...