AB = DA + DB and CB = EC + EB

DB = EB

AB = CB, DA = EC

DA + DB = EC + EB

Substitution

AE = CD

SSS (Side-Side-Side)

Substitution

CPCTC

△DAC = △ECA

Reflexive

Algebra

Reflexive

△DBC = △EBA

∠A = ∠C

SAS (Side-Angle-Side)

CPCTC

CB = DA + DB

EC + DB = EC + EB

∠B = ∠B

AC = AC

Given

Segment addition theorem

Substitution