We are given that sides JN and NL are congruent, and sides KN and MN are congruent. Angles 1 and 2 are vertical angles by definition. Therefore, they are congruent via the Vertical Angles Theorem. Since we now have a pair of corresponding, congruent sides, a pair of corresponding, congruent angles, and another pair of corresponding, congruent sides, we can apply the Side-Angle-Side Postulate. By SAS, triangles JKN and LMN are congruent.