在边AB上截取AG = AF,交AB于G
∵AD是∠BAC的平分线
且AF = AG
∴DF = DG
∴∠AFD = ∠AGD
∠AFD+∠AED+∠EDF+∠BAF=360°
∴∠AFD + ∠AED = 180°
∴∠AGD + ∠AED = 180°
∵∠AGD + ∠DGB = 180°
∴∠AED = ∠DGB
∴DG = DE
∴DF = DE
在边AB上截取AG = AF,交AB于G
∵AD是∠BAC的平分线
且AF = AG
∴DF = DG
∴∠AFD = ∠AGD
∠AFD+∠AED+∠EDF+∠BAF=360°
∴∠AFD + ∠AED = 180°
∴∠AGD + ∠AED = 180°
∵∠AGD + ∠DGB = 180°
∴∠AED = ∠DGB
∴DG = DE
∴DF = DE