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