考虑△ABC,AD为∠A的平分线.则CD/DB=AC/AB,因此CD/CB=AC/(AC+AB)作DE//AB交AC于E,则 DE/AB=CD/CB=AC/(AC+AB)所以 AE=DE=AB.AC/(AC+AB)若△A‘B’C‘中A'E'为∠A’平分线,且有AB=A‘B’,AC=A’C’,AD=A‘D’作D’E‘/...