What does HL mean to prove the congruence of two right triangles?

What does HL mean to prove the congruence of two right triangles?

Concept: two right triangles are congruent if one right side and the hypotenuse are equal

When proving the congruence of triangles with HL, can we prove that the right angle in RT △ XXX is equal to 90 degrees
As known, de ⊥ AC DF ⊥ ab
The process should write ∵ de ⊥ AC DF ⊥ ab
∴∠BFD ＝∠CDE＝90°
∵ in RT △ XXX and RT △ XXX
Or directly prove that in RT △ XXX ∵ de ⊥ AC DF ⊥ AB is not needed
It's the BFD = CDE = 90 ° one

Need that step, although it is in RT △ XXX, but still need to specify which angle is a right angle, right angle side and hypotenuse should be clear

The proof of "HL" theorem,
Theorem: the hypotenuse and a right angle side are congruent to the two triangles of the influence of the edge, etc

Because the hypotenuse is equal to one right angle, so is the other right angle (Pythagorean theorem)
A triangle is congruent (edge) because all corresponding edges are equal