△ABC中,AB=AC,点E在CA的延长线上,且∠AEF=∠AFE,试问直线EF和BC有何位置关系?为

∵AB＝AC∴∠BCA=∠ABC∵∠AEF＝∠AFE∠BAC=∠AEF+∠AFE∴ 在△ABC中∠BAC+∠BCA+∠ABC=180即∠AEF+∠AFE+∠BCA+∠ABC=180∠AFE+∠ABC=90∴EF⊥BC