Parallelograms

A parallelogram is a quadrilateral in which both pairs of opposite sides are parallel. This can be written as: In quadrilateral $ABCD$, if $AB \parallel CD$ and $AD \parallel BC$, then $ABCD$ is a parallelogram.

Important properties

• Opposite sides are equal in length: $AB = CD$ and $AD = BC$.

• Opposite angles are equal: $\angle A = \angle C$, $\angle B = \angle D$.

• The diagonals bisect each other.

• The sum of the angles is $360^\circ$.

• Each pair of adjacent angles adds up to $180^\circ$.