### Parallelograms

#### Definition of a parallelogram

A parallelogram is a quadrilateral whose opposite sides are parallel.

#### Properties of a parallelogram

- The opposite angles of a parallelogram are equal.
- The opposite sides of a parallelogram are equal.
- The diagonals of a parallelogram bisect each other.

#### Tests for a parallelogram

A quadrilateral is a parallelogram if:

- its opposite angles are equal, or
- its opposite sides are equal, or
- one pair of opposite sides are equal and parallel, or

its diagonals bisect each other.