问题转化为证：∠CFE=∠CEF∠CFE = ∠CAB + ∠FBA（三角形外角等于不想邻两内角和）∠CEF = ∠DCB + ∠CBF（同上）因为BF为平分∠ABC,故 ∠CBF = ∠FBA又有 ∠CAB + ∠ACD = ∠ACD + ∠DCB = 90°故 ∠CAB = ∠DCB ...
