A quadrilateral is a polygon the has exactly four sides. (This also means that a quadrilateral has exactly four vertices, and also exactly 4 angles.)

## Meaning

A quadrilateral is a polygon the has precisely four sides. (This also way that a square has specifically four vertices, and also exactly 4 angles.) Discussions of 2-D shapes sometimes refer just to the border (the line segments that type the edge of the figure) or come the internal as well. As soon as we talk around “dissecting” a parallelogram and also rearranging the components to type a rectangle in stimulate to determine the area the the parallelogram, we are clearly referring come the edges and also the interior. The usual interpretations of polygons, however, refer just to the line segments that form the edges of the polygon. Most of the time, context will make clean what you mean, however you need to remain conscious that in some cases you may need come clarify.

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Elementary school curricula typically have youngsters learn the surname of unique subsets of quadrilaterals with details features. Below we perform the distinct names. Watch the articles on each type for their definitions and special properties.

trapezoids (A and also J are “typical” examples, but all parallelograms also fit the meaning of trapezoids);parallelograms (E is the “typical” example, yet all rectangles and rhombuses additionally fit the an interpretation of parallelograms);rectangles (F is the “typical” example, yet all squares also fit the meaning of rectangles);rhombuses (C and D room the “typical” examples, but all squares likewise fit the definition of rhombuses);squares (B), the many special of castle all.

kites (G and, in some definitions H).

## What’s in a word?

quadri- (four) + -lateral (side) method “four-sided.”

Compare quadri- to Spanish cuatro. Lateral means “side” (think of football, for example).

## Classification

Just together triangles and also quadrilaterals are special species of polygons, over there are numerous subclasses of quadrilaterals.

Like every polygons that have much more than 3 sides, quadrilaterals can be convex choose these , , , or concave favor these , .

Quadrilaterals can be divide by even if it is or no their sides, angles, diagonals, or vertices have special properties. The category schemes taught in elementary institution involve the number of pairs that parallel sides, and the congruence the sides, and also whether or no all the angles are appropriate angles (all angles are congruent). The name of numerous of these special quadrilaterals are likewise typically part of the elementary school curriculum, though tiny else around the nature of these figures may it is in studied until high school. Elementary school typically has children learn the surname of

trapezoids (A and also J space “typical” examples, however all parallelograms likewise fit the an interpretation of trapezoids);parallelograms (E is the “typical” example, but all rectangles and rhombuses also fit the an interpretation of parallelograms);rectangles (F is the “typical” example, however all squares additionally fit the definition of rectangles);rhombuses (C and also D room the “typical” examples, however all squares additionally fit the an interpretation of rhombuses);squares (B), the many special of them all; and sometimeskites (G and some include H).

The square is also the surname of the consistent quadrilateral — one in which every sides space congruent and all angles are congruent.

Though the names the are offered to individual figures does no change, the method that they are grouped may depend ~ above the attributes used to type them. In the group scheme displayed above, parallelograms (B, C, D, E, and F) have actually a location of their own (the appropriate hand column), and even rhombuses (B, C, D) have actually a place (the bottom row), yet rectangles (F and B) aren’t distinguished from the others. In the category scheme below, rectangles (F and B) have the right hand obelisk to themselves, yet parallelograms space not grouped in a means that excludes A, which is not a parallelogram. Children in primary qualities often discover it difficult to assign anything (geometrical or otherwise) at the same time to 2 categories.<1> Casual language likewise treats shape-names as “exclusive” fairly than “inclusive.” Thus, casual language treats square and rectangle together distinct, quite than dealing with square together a special type of rectangle, as math does. Similarly, students tend to act rectangles and also parallelograms as disjoint classes, quite than seeing a rectangle as a special form of parallelograms.

Given 6 toy horses and 4 toy cows, and also asked whether there are much more horses or much more animals, really young children often prize “more horses” due to the fact that in classifying the playthings as “horses,” they, for the moment, exclude them together “animals,” even though, if individually asked whether horses are animals, they will certainly say yes.

Another possible method to share quadrilaterals is by examining their diagonals. This may be available for middle grade students who have actually learned around perpendicular lines and bisectors.

DiagonalsPerpendicularNot PerpendicularCongruentNot Congruent
BisectorNot BisectorBisectorNot Bisector
SquareSpecial KiteRectangleIsosceles Trapezoid

## Mathematical background

### Properties

The amount of the inner angles in a square is 360°. College student who know the analogous an outcome for triangles can convince themselves of this by cut a quadrilateral into two triangles by illustration a diagonal: each triangle includes 180° of edge measure, therefore the 2 triangles contain 360°.

Children can also experiment v this idea by

coloring or labeling the corners of a square ,cutting the corners turn off  , andfitting the colored vertices together to display that they all fit snugly around a point. Tesselation: The truth that the four vertices to the right snugly around a single point permits us to arrange four copies of a quadrilateral approximately a point. Nevertheless of the square one start with, four copies of it have the right to be i ordered it to right snugly around a solitary point. Multiple duplicates of the foursome will tile the plane. Even if one starts with a concave quadrilateral prefer this , one have the right to group four identical duplicates of them snugly roughly a point , and also can tile the entire plane with lot of copies. ### Special topics (rarely in elementary or middle school)

Cyclic quadrilaterals: For some quadrilaterals, it is feasible to pass a single circle v all four of the vertices. These special cases, dubbed cyclic quadrilaterals, encompass rectangles (and thus squares) and also isosceles trapezoids, but also other forms that have actually no unique name of your own. Cyclic quadrilaterals have actually the special residential property that the sum of your opposite angles is a right angle, or 180 degrees. The implication works in the other direction, too: any type of quadrilateral who opposite angles add up to 180 degrees is a cyclic quadrilateral. When the quadrilateral and the circle passing through its vertices are both shown, the square is claimed to it is in inscribed within the circle and the circle is claimed to be circumscribed around the quadrilateral.  Parallelograms that room not also rectangles cannot be enrolled in a circle: they space not cyclic quadrilaterals. A circle the passes through 3 of the vertices is either too huge to pass with the fourth (blue circle at the left) or too little to pass through the fourth (red circle at the right).

In enhancement to circumscribing circles around a square (drawing circles around a quadrilateral, poignant each vertex), it is sometimes possible to inscribe a circle (draw a circle within a quadrilateral so that each next of the quadrilateral is tangent to the circle). This team of quadrilaterals has no special name the its own, but includes kites, rhombuses, and squares in addition to other quadrilateral that have actually no specific name.

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Investigations: when investigating special quadrilaterals and also their properties, college student find plenty of ways to identify quadrilaterals. Some fertile explorations asking students to look for one-of-a-kind properties of angle (congruent or supplementary), sides (parallel, perpendicular, or congruent), and diagonals (perpendicular, bisecting, or congruent).