We have that the initial triangles are equal. Let us check which components remain within the final triangles as the same. The only such components are the angles B and C. We now know that we have to apply a triangle equality criterion.
The triangles BGH and CIH are equal since the have 2 common sides and the respective interior angles are equal. Then we have that BI=GC and also that the respective angles B and C are equal. THen also HIJ=HGJ since they fill to 180 degrees with angles that are equal.
Hence by angle-side-angle the triangles BJI and CJG are equal.
