This page examines the properties of two-dimensional or ‘plane’ polygons. A polygon is any kind of shape consisted of of straight lines that can be attracted on a flat surface, choose a item of paper. Such shapes encompass squares, rectangles, triangles and pentagons however not circles or any other form that consists of a curve.

You are watching: A three sided regular polygon is called equilateral

Understanding forms is vital in mathematics. Girlfriend will certainly be forced to learn around shapes in ~ school but understanding the nature of shapes has numerous practical applications in professional and also real-life instances too.

Many specialists need to understand the properties of shapes, consisting of engineers, architects, artists, real-estate agents, farmers and also construction workers.

You may well require to understand shapes once doing home improvements and DIY, as soon as gardening and even when planning a party.

When working through polygons the main properties i m sorry are necessary are:

The number that sides that the shape. The angles between the political parties of the shape. The length that the sides of the shape.

Number the Sides

Polygons space usually characterized by the number of sides that they have.

Three-Sided Polygons: Triangles

A three-sided polygon is a triangle. there are number of different types of triangle (see diagram), including:

Equilateral – all the sides are equal lengths, and all the interior angles room 60°. Isosceles – has two equal sides, with the third one a different length. Two of the internal angles space equal. Scalene – all three sides, and all three interior angles, are different.

Triangles can additionally be described in terms of their inner angles (see our page on Angles for more about naming angles). The inner angles that a triangle always add up come 180°.

A triangle through onlyacuteinternal angle is dubbed an acute (or acute-angled) triangle. One with oneobtuseangle and two acute angles is called obtuse (obtuse-angled), and one through aright angleis well-known as right-angled.

Each that these will certainly also be one of two people equilateral, isosceles or scalene.


Four-Sided polygons - Quadrilaterals

Four-sided polygons room usually described as quadrilaterals, quadrangles or periodically tetragons. In geometry the hatchet quadrilateral is commonly used.

The ax quadrangle is often used to define a rectangular enclosed out space, for instance ‘the freshers assembled in the university quadrangle’. The term tetragon is continual with polygon, pentagon etc. You might come throughout it occasionally, however it is not generally used in practice.

The family members of quadrilaterals includes the square, rectangle, rhombus and other parallelograms, trapezium/trapezoid and kite.

The internal angles of all quadrilaterals include up come 360°.


Square: four sides of equal length, four internal appropriate angles.

Rectangle: four internal appropriate angles, opposite sides of equal length.

Parallelogram: the opposite sides space parallel, the contrary sides room equal in length, the contrary angles are equal.

Rhombus: A special kind of parallelogram in i m sorry all 4 sides room the exact same length, prefer a square that has been squashed sideways.

Trapezium (or trapezoid): two sides room parallel, however the various other two sides room not. Next lengths and angles are not equal.

Isosceles Trapezium (or trapezoid): 2 sides space parallel and base angles room equal, definition that non-parallel political parties are additionally equal in length.

Kite: two pairs of adjacent sides space of same length; the shape has actually an axis that symmetry.

Irregular Quadrilateral: a four-sided shape where no sides are equal in length and no internal angles room the same. All inner angles still include up come 360°, just like all other continual quadrilaterals.

More than 4 Sides

A five-sided form is called a pentagon.

A six-sided shape is a hexagon, a seven-sided shape a heptagon, if an octagon has actually eight sides…

Polygon Names

The names of polygon are obtained from the prefixes of ancient Greek numbers. The Greek numerical prefix occurs in plenty of names of day-to-day objects and also concepts. These deserve to sometimes be helpful in helping you mental how plenty of sides a polygon has. Because that example:

an octopus has eight foot – an octagon has eight sides. A te is ten years – a decagon has ten sides. The contemporary pentathlon has five occasions – a pentagon has 5 sides. An Olympic heptathlon has seven events – a heptagon has seven sides.

The ‘poly-‘ prefix simply means ‘multiple’, therefore a polygon is a form with lot of sides, in the same method that ‘polygamy’ means multiple spouses.

There room names for numerous different varieties of polygons, and usually the number of sides is much more important 보다 the name of the shape.

There room two main species of polygon - regular and irregular.

A regular polygon has equal size sides with equal angles in between each side. Any type of other polygon is one irregular polygon, which by definition has unequal size sides and also unequal angles between sides.

Circles and shapes that include curves room not polygons - a polygon, by definition, is made up of right lines. See our pages top top circles and also curved shapes for more.


Angles between Sides

The angles in between the political parties of shapes are crucial when defining and working with polygons. Check out our page on angle for more about exactly how to measure angles.

There is a beneficial formula for finding out the total (or sum) of inner angles for any kind of polygon, that is:

(number of sides - 2) × 180°


For a pentagon (a five-sided shape) the calculation would certainly be:

5 - 2 = 3

3 × 180 = 540°.

The amount of inner angles for any type of (not complex) pentagon is 540°.

Furthermore, if the form is a regular polygon (all angles and also length the sides space equal) then you deserve to simply division the amount of the internal angles through the variety of sides to find each interior angle.

540 ÷ 5 = 108°.

A regular pentagon therefore has 5 angles each same to 108°.

The length of the Sides

As well together the variety of sides and the angles between sides, the length of each side of shapes is also important.

The size of the political parties of a aircraft shape allows you to calculation the shape’s perimeter (the distance about the exterior of the shape) and also area (the lot of room inside the shape).


If your form is a continuous polygon (such together a square in the example above) then it is only vital to measure up one side as, through definition, the various other sides that a consistent polygon room the very same length. That is typical to use tick marks to show that every sides are an same length.

In the example of the rectangle we required to measure two sides - the two unmeasured sides are equal to the 2 measured sides.

It is usual for some dimensions no to be displayed for more complicated shapes. In together cases missing dimensions have the right to be calculated.


In the example above, two lengths room missing.

The missing horizontal length have the right to be calculated. Take the shorter horizontal recognized length native the much longer horizontal well-known length.

9m - 5.5m = 3.5m.

The very same principle deserve to be provided to work out the lacking vertical length. That is:

3m - 1m = 2m.

Bringing all the information Together: Calculating the Area the Polygons

The simplest and most straightforward polygon for the purposes of calculating area is the quadrilateral. To acquire the area, you simply multiple length by vertical height.

For parallelograms, note that vertical elevation is NOT the size of the sloping side, however the upright distance in between the 2 horizontal lines.

This is due to the fact that a parallel is basically a rectangle v a triangle reduced off one end and also pasted onto the other:

You deserve to see that if you remove the left-hand blue triangle, and also stick the onto the other end, the rectangle i do not care a parallelogram.

The area is size (the peak horizontal line) multiplied by height, the vertical distance in between the two horizontal lines.

To work out the area the a triangle, friend multiple length by vertical height (that is, the vertical elevation from the bottom heat to the optimal point), and halve it. This is essentially because a triangle is fifty percent a rectangle.

To calculate the area of any kind of regular polygon, the easiest way is to divide it into triangles, and use the formula because that the area that a triangle.

So, for a hexagon, because that example:

You have the right to see from the diagram that there are 6 triangles.

The area is:

Height (red line) × size of next (blue line) × 0.5 × 6 (because there are 6 triangles).

You can additionally work the end the area of any kind of regular polygon making use of trigonometry, but that’s rather much more complicated.

See our page Calculating Area for more, consisting of examples.

You can likewise work out the area of any regular polygon making use of trigonometry, however that’s rather an ext complicated. View our Introduction come Trigonometry page for an ext information.

See more: How Much Is One Bouillon Cube S, 8 Ct / 3, Subbing Bouillon For Broth In Recipes

Continue to: Calculating AreaCurved Shapes

See also:Three-Dimensional shapes | Area, surface Area and Volume recommendation Sheet simple Transformations that 2-Dimensional shapes | positive and negative Numbers

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