Parallelogram Theorems

Here are a few theorems to find out if that pesky quadrilateral is a parallelogram. Remember that parallelograms must contain two pairs of parallel sides by definition. If a quadrilateral has two pairs of congruent angles or sides, it is a parallelogram. If there is one pair of sides that are parallel and congruent, it is a parallelogram. Finally if it has diagonals that bisect, it is a parallelogram.