SOLUTION
From the question given, the reasons for the prove of the following statements are correct so far.
For the last part
![\Delta GJK\cong\Delta IHK](https://img.qammunity.org/2023/formulas/mathematics/college/o4lk8n7j5ams9n4dvjuch7bf06beb0zhts.png)
The reason is Side-side-side theorem.
This theorem states that all three sides of a triangle are congruent (identical) to the corresponding sides of another triangle, then the triangles themselves are also congruent.
Hence the answer is Side-side-side theorem.