The HL triangle congruence states that two right triangles are equal if their hypothenuse and one of their legs are equal.
1. Considering the right triangles:
The sides that are marked with two tick marks are equal and the sides that are marked with three tick marks are equal.
So, the hypotenuse of both triangles is equal as well as the corresponding sides (marked b in the graph) which means that these triangles are congruent by HL