Rhombus
Type	Quadrilateral
Edges and vertices	4
Symmetry group	D2 (*2)
Dual polygon	Rectangle
Properties	convex, Isotoxal

In geometry, a rhombus or rhomb is a quadrilateral whose four sides all have the same length. The rhombus is often called a diamond, after the diamonds suit in playing cards, or a lozenge, though the latter sometimes refers specifically to a rhombus with a 45° angle.

In general, a polygon whose sides have the same length is called equilateral, so a rhombus is an equilateral quadrilateral. Every rhombus is a parallelogram, and a rhombus with right angles is a square. (Euclid's original definition and some English dictionaries' definition of rhombus exclude squares, but modern mathematicians prefer the inclusive definition.)^[1]

The English word “rhombus” derives from the Ancient Greek ῥόμβος (rhombos), meaning “spinning top”. The plural of rhombus can be either rhombi or rhombuses.

Contents 1 Properties 2 Area 3 Origin 4 Rhombus in mathematics 5 References 6 External links

[edit] Properties

Every rhombus has two diagonals connecting opposite pairs of vertices and two pairs of parallel sides. Using congruent triangles, one can prove that the rhombus is symmetric across each of these diagonals. It follows that any rhombus has the following two properties:

1. Opposite angles of a rhombus have equal measure.
2. The two diagonals of a rhombus are perpendicular.

The first property implies that every rhombus is a parallelogram. A rhombus therefore has all of the properties of a parallelogram: opposite sides are parallel, adjacent angles are supplementary, and the two diagonals bisect one another.

Not every parallelogram is a rhombus, though any parallelogram with perpendicular diagonals (the second property) is a rhombus. In general, any quadrilateral whose two diagonals are perpendicular is called a kite. Every rhombus is a kite, and any quadrilateral that is both a kite and parallelogram is a rhombus

[edit] Area

The area can be calculated as "base times perpendicular height" (as for a parallelogram) or as "half the product of the diagonals".

[edit] Origin

The word rhombus is from the Greek word for something that spins. Euclid used ρόμβος (rhombos), from the verb ρέμβω (rhembo), meaning "to turn round and round".^[2][3] Archimedes used the term "solid rhombus" for two right circular cones sharing a common base.^[4]

[edit] Rhombus in mathematics

• The dual polygon of a rhombus is a rectangle.
• One of the five 2D lattice types is the rhombic lattice, also called centered rectangular lattice.
• Three-dimensional analogues of a rhombus include the bipyramid and the bicone.

[edit] References

[edit] External links

Look up rhombus in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Rhombus

• Parallelogram and Rhombus - Animated course (Construction, Circumference, Area)
• Rhombus definition. Math Open Reference With interactive applet.
• Rhombus area. Math Open Reference Shows three different ways to compute the area of a rhombus, with interactive applet.