延长AE与BC的延长线交与M
AD‖BC
∠DaB+∠ABC=180°
AE,BE分别平分角DAB,角ABC
∠BAE+∠ABE=90°
∠AEB=90°
AD‖BC
∠DAE =∠M
∠BAE=∠M
∠AEB=∠MEB=90
△ABE≌△BME
AE=EM
△ADE≌△CEM
DE=CE