Answer:
HL theorem.
Explanation:
According to the image, the given triangles have congruent hypothenuse and a corresponding congruent leg, that means we need to use Hypothenuse-Leg theorem.
The Hypothenuse-Leg (HL) theorem states that if the triangles have congruent hypothenuse and a corresponding congruent leg, then those triangles are congruent.
This theorem is based on the definition about the right angle of a right triangle, that's why is only needed to elements to have a congruence.
Therefore, the answer is HL theorem.