下面是加拿大一道奥林匹克数学竞赛题: 如图1所示汤刀是△ABC一边BC上的中 线,F是边AB上任一点,连结C不,交AD于点 “( ab摊 ac+加一麟’ac+阮一溯 E,证明 ZAF BF 乃E DE. 这道赛题的证明并不 难,有趣的是其证法却很B 多,下面作简要的解答. 1.利用正弦定理 由两点间的距离公式即 The following is a Canadian Olympic math contest title: As shown in Figure 1, the soup knife is the midline of △ABC on one side of BC, F is any point on the side AB, link C is not, AD is at the point "(ab to share ac + plus a lin’ac + It is not difficult to prove that ZAF BF is E DE. The interesting proof is that the proof is very B. Here’s a brief explanation. 1. Use sine to determine the distance between two points. The formula is