We have to prove Δ ABC and Δ DEF are congruent or Δ ABC ≅ Δ DEF applying the Angle-Side-Angle or ASA rule.
In order to maintain the sequence, in ASA rule we have to make congruent two angles and one side in between them.
Therefore, if ∠ B and ∠ E are proved to be congruent and segment AB and segment DE are proved to be congruent, then we have to consider another two angles which must be ∠ A and ∠ D to be congruent.
