To prove that ΔDEF ≅ ΔDGF by SSS, what additional information is needed? 1. ∠DEF≅∠DGF
2. ∠DFE ≅ ∠DFG
3. DE ≅ DG
4. DG ≅ GF

3

Both triangles share the side in the middle, and the orange lines are markings that indicate those two sides of the triangles are equal length.

But SSS = side side side, meaning all 3 sides of both triangles must be equal to the side measurements of the opposite triangle. You have to chose an answer that shows congruence(equal value) on the last side of both triangles.

The last sides of each triangle are the segments DE and DG, so you choose the answer that sets DE = DG, choice 3.