You are given two pairs of triangles. For the first pair of triangles, each angle and side of one triangle is congruent to the corresponding angle and side of the other. You show that rigid motions can transform one triangle so that it matches up with the other. For the second pair of triangles, you show that rigid motions can transform one triangle so that each side or angle of one triangle matches exactly with a corresponding side or angle of the other triangle. What have you proved?