Rectangle facts for kids
Quick facts for kids Rectangle 


Rectangle


Type  quadrilateral, trapezium, parallelogram, orthotope 
Edges and vertices  4 
Schläfli symbol  { } × { } 
Coxeter diagram  
Symmetry group  Dihedral (D_{2}), [2], (*22), order 4 
Dual polygon  rhombus 
Properties  convex, isogonal, cyclic Opposite angles and sides are congruent 
In Euclidean plane geometry, a rectangle is a shape with for sides and four right angles. A rectangle with four sides of equal length is a square. The term oblong is occasionally used to refer to a nonsquare rectangle.
The word rectangle comes from the Latin rectangulus, which is a combination of rectus (as an adjective, right, proper) and angulus (angle).
Other geometries, such as spherical, elliptic, and hyperbolic, have socalled rectangles with opposite sides equal in length and equal angles that are not right angles.
Rectangles are involved in many tiling problems, such as tiling the plane by rectangles or tiling a rectangle by polygons.
Contents
Classification
Traditional hierarchy
A rectangle is a special case of a parallelogram in which each pair of adjacent sides is perpendicular.
A parallelogram is a special case of a trapezium (known as a trapezoid in North America) in which both pairs of opposite sides are parallel and equal in length.
A trapezium is a convex quadrilateral which has at least one pair of parallel opposite sides.
A convex quadrilateral is
 Simple: The boundary does not cross itself.
 Starshaped: The whole interior is visible from a single point, without crossing any edge.
Properties
Symmetry
A rectangle is cyclic: all corners lie on a single circle.
It is equiangular: all its corner angles are equal (each of 90 degrees).
It is isogonal or vertextransitive: all corners lie within the same symmetry orbit.
It has two lines of reflectional symmetry and rotational symmetry of order 2 (through 180°).
Rectanglerhombus duality
The dual polygon of a rectangle is a rhombus, as shown in the table below.
Rectangle  Rhombus 

All angles are equal.  All sides are equal. 
Alternate sides are equal.  Alternate angles are equal. 
Its centre is equidistant from its vertices, hence it has a circumcircle.  Its centre is equidistant from its sides, hence it has an incircle. 
Two axes of symmetry bisect opposite sides.  Two axes of symmetry bisect opposite angles. 
Diagonals are equal in length.  Diagonals intersect at equal angles. 
 The figure formed by joining, in order, the midpoints of the sides of a rectangle is a rhombus and vice versa.
Formulae
If a rectangle has length and width
Theorems
The isoperimetric theorem for rectangles states that among all rectangles of a given perimeter, the square has the largest area.
The midpoints of the sides of any quadrilateral with perpendicular diagonals form a rectangle.
A parallelogram with equal diagonals is a rectangle.
The Japanese theorem for cyclic quadrilaterals states that the incentres of the four triangles determined by the vertices of a cyclic quadrilateral taken three at a time form a rectangle.
The British flag theorem states that with vertices denoted A, B, C, and D, for any point P on the same plane of a rectangle:
Crossed rectangles
A crossed quadrilateral (selfintersecting) consists of two opposite sides of a nonselfintersecting quadrilateral along with the two diagonals. Similarly, a crossed rectangle is a crossed quadrilateral which consists of two opposite sides of a rectangle along with the two diagonals. It has the same vertex arrangement as the rectangle. It appears as two identical triangles with a common vertex, but the geometric intersection is not considered a vertex.
A crossed quadrilateral is sometimes likened to a bow tie or butterfly, sometimes called an "angular eight". A threedimensional rectangular wire frame that is twisted can take the shape of a bow tie.
The interior of a crossed rectangle can have a polygon density of ±1 in each triangle, dependent upon the winding orientation as clockwise or counterclockwise.
A crossed rectangle may be considered equiangular if right and left turns are allowed. As with any crossed quadrilateral, the sum of its interior angles is 720°, allowing for internal angles to appear on the outside and exceed 180°.
A rectangle and a crossed rectangle are quadrilaterals with the following properties in common:
 Opposite sides are equal in length.
 The two diagonals are equal in length.
 It has two lines of reflectional symmetry and rotational symmetry of order 2 (through 180°).
Other rectangles
In spherical geometry, a spherical rectangle is a figure whose four edges are great circle arcs which meet at equal angles greater than 90°. Opposite arcs are equal in length. The surface of a sphere in Euclidean solid geometry is a nonEuclidean surface in the sense of elliptic geometry. Spherical geometry is the simplest form of elliptic geometry.
In elliptic geometry, an elliptic rectangle is a figure in the elliptic plane whose four edges are elliptic arcs which meet at equal angles greater than 90°. Opposite arcs are equal in length.
In hyperbolic geometry, a hyperbolic rectangle is a figure in the hyperbolic plane whose four edges are hyperbolic arcs which meet at equal angles less than 90°. Opposite arcs are equal in length.
Squared, perfect, and other tiled rectangles
A rectangle tiled by squares, rectangles, or triangles is said to be a "squared", "rectangled", or "triangulated" (or "triangled") rectangle respectively. The tiled rectangle is perfect if the tiles are similar and finite in number and no two tiles are the same size. If two such tiles are the same size, the tiling is imperfect. In a perfect (or imperfect) triangled rectangle the triangles must be right triangles. A database of all known perfect rectangles, perfect squares and related shapes can be found at squaring.net. The lowest number of squares need for a perfect tiling of a rectangle is 9 and the lowest number needed for a perfect tilling a square is 21, found in 1978 by computer search.
A rectangle has commensurable sides if and only if it is tileable by a finite number of unequal squares. The same is true if the tiles are unequal isosceles right triangles.
The tilings of rectangles by other tiles which have attracted the most attention are those by congruent nonrectangular polyominoes, allowing all rotations and reflections. There are also tilings by congruent polyaboloes.
See also
In Spanish: Rectángulo para niños
Victor J. Glover 
Yvonne Cagle 
Jeanette Epps 
Bernard A. Harris Jr. 