已知,ad = cd ,可得：∠bac = ∠acd ,所以,∠bdc = ∠bac+∠acd = 2∠bac ；已知,cd = bc ,可得：∠abc = ∠bdc ,所以,∠abc = 2∠bac ,即有：∠bac = (1/2)∠abc ；又已知,ab = ac ,可得：∠acb = ∠abc .在△abc中...