Answer: The HL Theorem.
Step-by-step explanation: We are given that the triangles have a congruent 90 degree angle and two congruent sides. This would indicate towards SAS but in this case, that doesn't work because the angle is not in between the two congruent sides. We know that the triangles are right, and that their hypotenuses are congruent and that one leg is congruent. Thus, the answer must be HL (hypotenuse & leg).