取BC中点G,连FG交EC于H、连EG得EG=GC,FDCD是菱形∴∠皮空知DFC=∠GFC∵亏判∠CGH=∠CEB=90°∴FG是燃消EC的垂直平分线∴∠GFE=∠GFC∵∠AEF=∠GFE∴∠AFE=∠GFE=∠GFC=∠DFC∴∠EFD=3∠AFE∴k=3
E F