b交于点h。是说明bh=cf的理由
∵AD是∠BAC,∴∠DAB=∠DAC, ∵E是BC的中点,∴BE=CE,∵EF∥AD,∴ΔACD∽ΔFCE,ΔBHE∽ΔBAD,∴∠DAC=∠EFC,∠DAB=∠EHB=∠FHA,∴AF=AH,FA:FC=ED:EC,HA:BH=ED:BE,∵EC=BE,∴FA:FC=HA:BH,∵FA=HA,∴BH=CF。