Answer:
What additional information do you need to prove ∆ ABC ≅ ∆ def by the SSS postulate description? So, △ABC ≅ △DEF. If three sides of one triangle are congruent to three sides of a second triangle, then the two triangles are congruent. If — AB ≅ — DE, — BC ≅ — EF, and — AC ≅ — DF, then △ABC ≅ △DEF.