Slope of KL = 2/2 = 1.
Slope of MN = 2/2 = 1.
Slope of LM = -1/2.
Slope of NK = -1/2.
The slopes of opposite sides KL and MN are equal.
The slopes of opposite sides LM and NK are equal.
Since quadrilateral KLMN has two pairs of opposite sides that are parallel, it is a parallelogram.