Junior one mathematics super problem! BD is the middle line of △ ABC, CE is perpendicular to BD at e, AF is perpendicular to BD, and the extension line of BD is at F. please specify: be + BF = 2bd

Junior one mathematics super problem! BD is the middle line of △ ABC, CE is perpendicular to BD at e, AF is perpendicular to BD, and the extension line of BD is at F. please specify: be + BF = 2bd

∵CE⊥BD AF⊥BD
∴∠CED=∠AFD
∵ BD is the middle line of △ ABC
∴AD=CD
In △ CED and △ AFD
∠CDE=∠ADF
AD=CD
∠CED=∠AFD
∴△CED≌△AFD
∴DE=DF
∴BD-DE+BD+DF=BE+BF=2BD