1.如图5-3-12,△ABC中,DE//BC,DF//AC,AF与DE交与点M,BE与DF交与N,求证:MN//AB

问题描述:

1.如图5-3-12,△ABC中,DE//BC,DF//AC,AF与DE交与点M,BE与DF交与N,求证:MN//AB

四边形EDFC 是平行四边形,DF=CE
△AME和△DMF中
AE:DF=EM:MD
AE:CE=EM:MD
NF‖CE
EN:BN =CF:B F=AD :BD =AE :EC
EN:BN =EM:MD
MN ‖AB