作DG平行于CF交AB于G
由于DG//CF => BG/GF = BD/DC. (又因为D为BC中点,所以 BD=DC),所以BG/GF = 1:1
同理由于DG//CF => AF/FG = AE/ED (E 为 AD中点 => AE=ED),所以AF/FG = 1:1
所以AF/GF/BG = 1:1:1,所以AF/BF = AF/(GF+BG) = 1:(1+1) = 1:2
跟上面推理过程一样,这一问的不同之处在于AE/ED 不为1:1了,可以设AE/AD = x:1 (0
即AF/FG=1:(1-x).
由于根据第一问的结论,FG=BG,所以AF/BF = AF/(GF+BG) =1:(1-x + 1-x) = 1:(2-2x)
其中x为AE/AD的值