Assume you are given two right triangle with congruent hypotenuses and wish to show that they are congruent

If you can find one leg of a triangle to be congruent to a leg on the other triangle, then you can use the HL (hypotenuse leg) theorem. If the hypotenuse and one leg of a right triangle are congruent to the hypotenuse and a leg of another right triangle, then the triangles are congruent.