Perimeter

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This article is about the distance around an object. For the freeway around Atlanta, Georgia, see Interstate 285.

The perimeter is the distance around a given two-dimensional object. The word perimeter is a Greek root meaning measure around, or literally "around measure".

1 Practical uses
2 Formulas
3 See also
4 External links

[edit] Practical uses

Calculations of perimeter and area have considerable practical applications. Perimeter is used in calculating the border of an object such as a yard or flowerbed when a fence or other border is being installed around the edges. Area is used when all the area inside of a perimeter is being covered with something, such as a yard being covered with sod or fertilizer.

In military usage, the term perimeter defines a geographic area of importance, such as a physical installation or defensive work, but can also refer to a theoretical construct such as an all-round defense formed by a small group of soldiers, the purpose of which is mutual protection of each other rather than defence of actual territory.

[edit] Formulas

[edit] Polygons

As a general rule, the perimeter of a polygon can always be calculated by adding all the length of the sides together. So, the formula for triangles is $P = a + b + c$ , where $a$ , $b$ and $c$ stand for each side of it. For quadrilaterals the equation is $P = a + b + c + d$ . For equilateral polygons, $P = n a$ , where n is the number of sides and a is the measure of the side.

[edit] Circles

For circles the equation is

$P = 2 \cdot pi \cdot r$

$P = d \cdot \pi$

$P$ stands for the perimeter,
$r$ stands for the radius
$π$ is the mathematical constant pi ( $π = 3.14159265...$ )
$d$ stands for the circle's diameter (twice the radius of a circle)

(The dot means multiply or times)

[edit] In General

If r is considered to be the distance from the center of a regular polygon to one of its vertices (or in the case of a circle, the radius), the following holds true:

$P = \frac{dA}{dr}$