∵AB=AC, point D.E is the bisector of BC, and AD=AE.
∴BD=EC
∴BD+DE=CE+DE means.
△ABE?△ACD
2
∫AB//DC, AD//BC
∴∠MPD=∠QNB,∠M=∠Q
MN = PQ
Mn+NP = PQ+NP means MP=NQ.
∴△MDP≌△QBN
∴DP=BN