从F做FP平行AC,交BD于P
FP‖AC,∴∠DAE=∠PFE.
AE=FE,∠AED=∠FEP
△ADE≌△FPE,FP=AD.FP:CD=1:2
FP‖CD简单有△BFP∽△BCD
FP:CD=BF:FC=1:2