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

Meaning

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

Discussions of 2-D shapes periodically refer just to the border (the line segments that kind the edges of the figure) or to the inner as well. When we talk around “dissecting” a parallelogram and also rearranging the components to kind a rectangle in bespeak to identify the area that the parallelogram, we are clearly referring to the edges and the interior. The usual definitions of polygons, however, refer only to the line segments that type the edge of the polygon. Many of the time, context will make clear what girlfriend mean, yet you must remain conscious that in some instances you might need to clarify.

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Elementary college curricula commonly have youngsters learn the names of unique subsets of quadrilateral with particular features. Right here we list the special names. Watch the posts on each kind for your definitions and special properties.

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

Some K-8 curricula likewise include

kites (G and, in some interpretations H).

What’s in a word?

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

Compare quadri- to Spanish cuatro. Lateral way “side” (think the football, because that example).

Classification

Just as triangles and quadrilaterals room special types of polygons, there are numerous subclasses the quadrilaterals.

Like every polygons that have more than three sides, quadrilaterals can be convex choose these

,
,
,
or concave favor these
,
.

Quadrilaterals can be share by even if it is or no their sides, angles, diagonals, or vertices have actually special properties. The classification schemes teach in elementary institution involve the number of pairs the parallel sides, and the congruence the sides, and whether or not all the angles are appropriate angles (all angles room congruent).

The surname of many of these one-of-a-kind quadrilaterals are also typically component of the elementary curriculum, though little else about the nature of these figures may it is in studied until high school. Elementary school school frequently has youngsters learn the names of

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

The square is additionally the name of the constant quadrilateral — one in which every sides space congruent and all angles are congruent.

Though the names the are offered to individual numbers does not change, the way that they space grouped may depend ~ above the features used to sort them. In the category scheme shown above, parallelograms (B, C, D, E, and also F) have actually a location of their own (the right hand column), and even rhombuses (B, C, D) have actually a ar (the bottom row), however rectangles (F and B) aren’t differentiated from the others. In the group scheme below, rectangles (F and B) have the right hand shaft to themselves, but parallelograms room not grouped in a method that excludes A, i beg your pardon is no a parallelogram.

Children in primary qualities often discover it hard to entrust anything (geometrical or otherwise) concurrently to two categories.<1> Casual language additionally treats shape-names together “exclusive” quite than “inclusive.” Thus, casual language treats square and rectangle as distinct, fairly than treating square together a special sort of rectangle, as math does. Similarly, students often tend to treat rectangles and parallelograms together disjoint classes, fairly than see a rectangle as a special type of parallelograms.

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

Another possible method to classify quadrilaterals is by assessing their diagonals. This may be obtainable for center grade student who have learned about perpendicular lines and also bisectors.

DiagonalsPerpendicularNot PerpendicularCongruentNot Congruent
BisectorNot BisectorBisectorNot Bisector
SquareSpecial KiteRectangleIsosceles Trapezoid

Mathematical background

Properties

The sum of the inner angles in a square is 360°. Students who know the analogous an outcome for triangles deserve to convince themselves of this by cutting a quadrilateral into two triangle by drawing a diagonal: each triangle consists of 180° of edge measure, therefore the two triangles save 360°.

Children can additionally experiment with this idea by

coloring or labeling the corners of a square
,cutting the corners off
, andfitting the fancy vertices together to present that they all fit snugly roughly a point.

Tesselation: The fact that the four vertices right snugly roughly a solitary point enables us come arrange four duplicates of a quadrilateral about a point. Regardless of the square one starts with, four duplicates of it deserve to be i ordered it to to the right snugly about a single point.

Multiple duplicates of the foursome will certainly tile the plane.
Even if one starts through a concave quadrilateral like this
, one have the right to group 4 identical duplicates of castle snugly about a allude
, and also can brick the entire plane with lot of copies.

Special topics (rarely in primary school or center school)

Cyclic quadrilaterals: For part quadrilaterals, it is possible to happen a single circle with all 4 of its vertices. These one-of-a-kind cases, called cyclic quadrilaterals, include rectangles (and therefore squares) and also isosceles trapezoids, but likewise other shapes that have actually no special name of their own. Cyclic quadrilaterals have the special home that the sum of their opposite angle is a directly angle, or 180 degrees. The implication works in the various other direction, too: any quadrilateral whose opposite angles add up come 180 degrees is a cyclic quadrilateral.

When the quadrilateral and also the circle passing with its vertices room both shown, the square is claimed to be inscribed in ~ the circle and also the one is said to be circumscribed about the quadrilateral.

Parallelograms that room not additionally rectangles can not be inscriptions in a circle: they room not cyclic quadrilaterals. A circle the passes through 3 of the vertices is one of two people too large to pass through the fourth (blue circle in ~ the left) or too tiny to pass through the 4th (red circle at the right).

In addition to circumscribing circles roughly a square (drawing circles approximately a quadrilateral, touching each vertex), the is sometimes possible to inscribe a circle (draw a circle in ~ a quadrilateral so the each side of the quadrilateral is tangent to the circle). This group of quadrilaterals has actually no unique name that its own, however includes kites, rhombuses, and squares together with other square that have actually no certain name.

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Investigations: when investigating special quadrilaterals and also their properties, college student find countless ways to differentiate quadrilaterals. Some fertile explorations asking students come look for unique properties of angles (congruent or supplementary), sides (parallel, perpendicular, or congruent), and also diagonals (perpendicular, bisecting, or congruent).