Exercise 68 Page 657

To prove that a quadrilateral is a parallelogram, it is enough to show that one of the following conditions is satisfied.

• Both pairs of opposite sides are parallel.
• Both pairs of opposite sides are congruent.
• Both pairs of opposite angles are congruent.
• The diagonals bisect each other.
• A pair of opposite sides is both parallel and congruent.

Let's analyze the given quadrilateral.

By looking at the diagonals, we can see both diagonals bisect each other. Recall that for a quadrilateral to be a parallelogram, both diagonals must be bisected. Therefore, it is a parallelogram.