# Geometry/Parallelograms
## Parallelograms

A parallelogram is a geometric figure with two pairs of parallel sides. Parallelograms are a special type of quadrilateral. The opposite sides are equal in length and the opposite angles are also equal. The area is equal to the product of any side and the distance between that side and the line containing the opposite side.

## Properties of Parallelograms

The following properties are common to all parallelograms (parallelogram, rhombus, rectangle, square)
* 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
* consecutive angles are supplementary

## Special Parallelograms
### Rhombus

* A rhombus is a parallelogram with four congruent sides.
* The diagonals of a rhombus are perpendicular.
* Each diagonal of a rhombus bisects two angles the rhombus.
* A rhombus may or may not be a square.

### Square

* A square is a parallelogram with four right angles and four congruent sides.
* A square is both a rectangle and a rhombus and inherits all of their properties.

### Navigation

* Geometry
* Part I—Euclidean Geometry:
** Chapter 1. Geometry/Points, Lines, Line Segments and Rays
** Chapter 2. Geometry/Angles
** Chapter 3. Geometry/Properties
** Chapter 4. Geometry/Inductive and Deductive Reasoning
** Chapter 5. Geometry/Proof
** Chapter 6. Geometry/Five Postulates of Euclidean Geometry
** Chapter 7. Geometry/Vertical Angles
** Chapter 8. Geometry/Parallel and Perpendicular Lines and Planes
** Chapter 9. Geometry/Congruency and Similarity
** Chapter 10. Geometry/Congruent Triangles
** Chapter 11. Geometry/Similar Triangles
** Chapter 12. Geometry/Quadrilaterals
** Chapter 13. Geometry/Parallelograms
** Chapter 14. Geometry/Trapezoids
** Chapter 15. Geometry/Circles/Radii, Chords and Diameters
** Chapter 16. Geometry/Circles/Arcs
** Chapter 17. Geometry/Circles/Tangents and Secants
** Chapter 18. Geometry/Circles/Sectors
** Appendix A. Geometry/Postulates & Definitions
** Appendix B. Geometry/The SMSG Postulates for Euclidean Geometry
* Part II—Coordinate Geometry:
** Geometry/Synthetic versus analytic geometry
* Two and Three-Dimensional Geometry and Other Geometric Figures
** Geometry/Perimeter and Arclength
** Geometry/Area
** Geometry/Volume
** Geometry/Polygons
** Geometry/Triangles
** Geometry/Right Triangles and Pythagorean Theorem
** Geometry/Polyominoes
** Geometry/Ellipses
** Geometry/2-Dimensional Functions
** Geometry/3-Dimensional Functions
** Geometry/Area Shapes Extended into 3rd Dimension
** Geometry/Area Shapes Extended into 3rd Dimension Linearly to a Line or Point
** Geometry/Polyhedras
** Geometry/Ellipsoids and Spheres
** Geometry/Coordinate Systems (currently incorrectly linked to Astronomy)
* Traditional Geometry:
** Geometry/Topology
** Geometry/Hyperbolic and Elliptic Geometry
** Geometry/Projective Geometry
** Geometry/Neutral Geometry
** Geometry/Inversive Geometry
* Modern geometry
** Geometry/Unified Angles
** Geometry/Groups
** Geometry/Algebraic Geometry
** Geometry/Differential Geometry
** Geometry/Algebraic Topology
** Geometry/Noncommutative Geometry
* Geometry/An Alternative Way and Alternative Geometric Means of Calculating the Area of a Circle