Examining the diagram, we see that two sides and the included angle of △ HKJ are congruent with two sides and the included angle of △ LNM. This means we can use the SAS Congruence Theorem to prove that these triangles are congruent.
When we know the triangles are congruent, we can identify corresponding parts. For example, we see that ∠ J and ∠ M are congruent. Also, note that ∠ K and ∠ N both help create the side that's marked with ||. Therefore we know these angles are congruent.
