A parallelogram
is a quadrilateral with both pairs of opposite sides parallel. The
opposite sides of a parallelogram are equal in length and the opposite
angles are equal. The diagonals cut each other in half.

All parallelograms
have rotational symmetry about the point of intersection of their
diagonals.

- Each diagonal bisects the parallelogram into two congruent triangles.
- The area of a parallelogram is twice the area of a triangle created by one of its diagonals.
- The area of a parallelogram is also equal to the magnitude of the vector cross product of two adjacent sides.
- Opposite angles of a parallelogram are equal.
- Opposite sides of a parallelogram are equal.
- The diagonals of a parallelogram bisect each other.