On a coordinate plane, quadrilateral H I J K is shown. Point H is at (0, 5), point I is at (3, 3), point J is at (4, negative 1), and point K is at (1, 1).
The coordinates of the vertices for the figure HIJK are H(0, 5), I(3, 3), J(4, –1), and K(1, 1).

To determine if it is a parallelogram, use the converse of the parallelogram diagonal theorem. This states that if the diagonals , then the quadrilateral is a parallelogram.

The midpoint of HJ is and the midpoint of IK is (2, 2).

Therefore, HIJK is a parallelogram because the diagonals , which means they bisect each other.