Given: AB = CB, DA = EC

Prove: ∠A = ∠C

CPCTC
△DAC = △ECA
Substitution
SAS (Side-Angle-Side)
Substitution
DA + DB = EC + EB
Reflexive
∠A = ∠C
Algebra
SSS (Side-Side-Side)
△DBC = △EBA
CPCTC
AB = DA + DB and CB = EC + EB
AE = CD
Reflexive
AB = CB, DA = EC
DB = EB
CB = DA + DB
EC + DB = EC + EB
∠B = ∠B
AC = AC
Given
Segment addition theorem
Substitution