如题所述
过E点作EG∥AF,过B点作BH∥AF
∠A=∠ABH,∠C=∠CBH
∠F=∠FEG,∠D=∠DEG
∠A+∠C+∠FED=∠ABH+∠CBH+∠F+∠D=∠ABC+∠F+∠D
得证
要具体步骤
求采纳