证明:
过E作AB的平行线交BC的延长线于F,
AB=AC,↔∠B=∠ACB,
∴∠F=∠B=∠ACB=∠ECF,
∴EC=EF=BD,
∵AB//EF,
∴DP/PE=BD/EF=EC/EF=1,
∴DP=PE