If two sides and the included angle of a triangle are congruent to two sides and the included angle of another triangle, then the two triangles are congruent.
In the figure, A B ¯ ≅ D E ¯ , B C ¯ ≅ E F ¯ , and ∠ B ≅ ∠ E .
Therefore, by the SAS postulate, Δ A B C ≅ Δ D E F .
