By SAS criterion ∆FGH ≅ ∆HIF.
What is congruence?
Congruent triangles share identical shape and size. They can be proven congruent by satisfying criteria such as Side-Angle-Side, Side-Side-Side, Angle-Side-Angle, Angle-Angle-Side, or Hypotenuse-Leg, establishing corresponding equalities in sides and angles between the triangles.
To prove ∆FGH ≅ ∆HIF
Proof:
1) FI ≅ GH (Given)
2) FH ≅ FH (Reflective property of congruence)
3) ∠GFH ≅ ∠IHF (Given)
4) ∆FGH ≅ ∆HIF(Side-Angle-Side SAS)
Therefore, by SAS criterion ∆FGH ≅ ∆HIF.