Hypotenuse Leg theorem states a condition for two right triangles to be congruent. Generally to check for triangle congruence three corresponding parts are considered. In the case of right triangles, as one corresponding part the right angle is implied in the name, the names of congruence criteria consist of only two parts as hypotenuse leg in this case. The theorem is also known shortly as HL Theorem.
let us state, prove the hypotenuse leg theorem and solve few problems based on the theorem.

If the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and a leg of another right triangle, then the two triangles are congruent.

Hypotenuse Leg Theorem

If Δs ABC and DEF are right triangles and leg AB ≅ leg DE and hypotenuse AC = hypotenuse DF,
then ΔABC ≅ ΔDEF.