Question

What additional information do you need to prove that ∆LMO ≅ ∆LNO by the HL Theorem? ∠NLO ≅ ∠MLO ∠MOL ≅ ∠NOL

Answer 1

For a better understanding of the solution given here please find the diagram in the file attached.

We know from the Hypotenuse Leg Theorem (the HL theorem) that "if the hypotenuse and one leg of a right triangle are congruent to the hypotenuse and one leg of another right triangle, then the triangles are congruent."

Thus, as can be seen from the diagram, Side LO (also called leg LO) is common to both the triangles LMO and LNO. Therefore, the additional information that will be required to prove the congruence is that the respective hypotenuses, MO and NO are equal.

Answer 2

The hypotenuse leg theorem states that any two right triangles that have a congruent hypotenuse and a corresponding, congruent leg are congruent triangles.
The triangles ΔLNO and ΔLMO have the same leg Lo, therefore you need the equality of hypotenuses LM=LN.