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

## Meaning

A square is a polygon that has exactly four sides. (This also way that a quadrilateral has exactly four vertices, and exactly four angles.) Discussions that 2-D shapes sometimes refer just to the border (the heat segments that kind the edges of the figure) or to the interior as well. As soon as we talk about “dissecting” a parallelogram and also rearranging the parts to form a rectangle in bespeak to identify the area of the parallelogram, us are plainly referring come the edges and also 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 you mean, but you should remain mindful that in some cases you may need come clarify.

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Elementary college curricula generally have youngsters learn the surname of special subsets of square with particular features. Right here we list the distinct names. Check out the articles on each kind for your definitions and also special properties.

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

Some K-8 curricula likewise include

kites (G and, in some meanings H).

## What’s in a word?

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

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

## Classification

Just as triangles and quadrilaterals are special types of polygons, there are countless subclasses that quadrilaterals.

Like all polygons the have more than three sides, quadrilaterals can be convex prefer these , , , or concave prefer these , .

Quadrilaterals have the right to be divide by even if it is or no their sides, angles, diagonals, or vertices have actually special properties. The category schemes teach in elementary college involve the variety of pairs of parallel sides, and the congruence the sides, and also whether or not all the angle are appropriate angles (all angles room congruent). The name of many of these special quadrilaterals are likewise typically part of the elementary school curriculum, though small else around the properties of these figures may be studied until high school. Elementary school typically has children learn the name of

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

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

Though the names that are offered to individual figures does not change, the way that they space grouped might depend ~ above the characteristics used to kind them. In the classification scheme displayed above, parallelograms (B, C, D, E, and also F) have a ar of their very own (the best hand column), and also even rhombuses (B, C, D) have actually a ar (the bottom row), however rectangles (F and also B) aren’t differentiated from the others. In the category scheme below, rectangles (F and B) have the ideal hand column to themselves, but parallelograms room not group in a method that excludes A, i beg your pardon is not a parallelogram. Children in primary grades often discover it hard to assign anything (geometrical or otherwise) all at once to two categories.<1> Casual language also treats shape-names as “exclusive” rather than “inclusive.” Thus, casual language treats square and rectangle together distinct, fairly than dealing with square as a special sort of rectangle, as math does. Similarly, students tend to treat rectangles and parallelograms as disjoint classes, fairly than seeing a rectangle as a special type of parallelograms.

Given 6 toy horses and also 4 toy cows, and also asked whether there are an ext horses or an ext animals, really young children often price “more horses” because in classifying the toys as “horses,” they, for that moment, exclude, them together “animals,” even though, if individually asked whether equines are animals, they will certainly say yes.

Another possible means to divide quadrilaterals is by assessing their diagonals. This might be easily accessible for middle grade college student who have 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 quadrilateral is 360°. Student who understand the analogous result for triangles have the right to convince themselves of this by cutting a quadrilateral into two triangle by illustration a diagonal: every triangle contains 180° of angle measure, for this reason the 2 triangles contain 360°.

Children can additionally experiment v this idea by

coloring or labeling the corners the a square ,cutting the corners turn off  , andfitting the fancy vertices together to present that they every fit snugly approximately a point. Tesselation: The reality that the four vertices fit snugly roughly a solitary point permits us to arrange four duplicates of a quadrilateral about a point. Nevertheless of the square one starts with, four copies of it have the right to be arranged to fit snugly around a single point. Multiple duplicates of that foursome will tile the plane. Even if one starts through a concave quadrilateral favor this , one have the right to group 4 identical copies of lock snugly around a point , and can tile the entire aircraft with many copies. ### Special topics (rarely in elementary school or middle school)

Cyclic quadrilaterals: For some quadrilaterals, the is possible to happen a solitary circle through all four of that is vertices. These special cases, referred to as cyclic quadrilaterals, incorporate rectangles (and thus squares) and isosceles trapezoids, but likewise other shapes that have no special name of their own. Cyclic quadrilaterals have the special property that the sum of your opposite angle is a straight angle, or 180 degrees. The implication functions in the other direction, too: any type of quadrilateral whose opposite angles include up come 180 levels is a cyclic quadrilateral. When the quadrilateral and also the circle passing with its vertices are both shown, the quadrilateral is stated to it is in inscribed in ~ the circle and the circle is claimed to it is in circumscribed about the quadrilateral.  Parallelograms that room not additionally rectangles cannot be inscribed in a circle: they space not cyclic quadrilaterals. A circle that passes through 3 of the vertices is one of two people too big to pass with the fourth (blue circle in ~ the left) or too small to pass through the 4th (red circle in ~ the right).

In addition to circumscribing circles approximately a square (drawing circles about a quadrilateral, poignant each vertex), it is sometimes feasible to inscribe a circle (draw a circle within a quadrilateral so the each next of the quadrilateral is tangent come the circle). This group of quadrilaterals has actually no distinct name the its own, however includes kites, rhombuses, and squares along with other square that have actually no particular name.

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