# How to calculate the perimeter?

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We often heard from teachers: "Do your best, knowledge will be very useful in your life," and, indeed, this happens. For example, when we undertake repair, it is absolutely necessary for us to know how to calculate the perimeter of a particular figure in order to determine the required amount of building material. In this article for those who have forgotten the school course, we will talk about how to calculate the perimeter of various figures.

## What is the perimeter?

The perimeter is the length of a line delineating a geometric figure; length of all sides of a flat figure. Thus, to find the perimeter of the figure, it is enough to measure the length of each side and add up all the results. However, sometimes it is possible to make the calculation in a simpler way using special formulas. Next, we analyze ways to find the perimeter of various shapes using both methods.

## Perimeter of a triangle

Before calculating the perimeter of a triangle, it is necessary to measure the length of each side. After that, simply fold them - this will be the perimeter.

However, if we are dealing with an isosceles triangle, we can measure one of the equal sides and multiply the value obtained by two, and then add the length of the base to it.

To calculate the perimeter of an equilateral triangle, it is sufficient to measure only one side at all and multiply the value obtained by three.

## Perimeter of a quadrilateral

We will analyze in this section how to calculate the perimeter of a square, a rhombus, a rectangle, a parallelepiped and a trapezium.

### Square and rhombus

As you know, the square has four sides and they are all equal, which means that to calculate the perimeter of the square, you need to measure one of its sides, and then multiply the resulting value by 4. Strictly speaking, the perimeter of the rhombus is exactly the same, because the diamond has all are equal.

### Rectangle and parallelogram

At the rectangle, the sides are equal in pairs, thus, to calculate the perimeter, you need to measure the larger and smaller sides, multiply each of the obtained values by two and add the resulting values. Similarly, the perimeter of the parallelogram.

### Trapezium

Another type of quad is a trapezium.In this figure, as a rule, all sides are of different lengths, and therefore to find the perimeter it is necessary to measure each side and put them together. However, the trapezoid can be isosceles. In this case, to calculate the perimeter, you can use the following formula: P = a + b + 2c, where c is the length of one of the equal sides.

There is, by the way, another way to determine the perimeter of an isosceles trapezium - the so-called "midline method". First you need to draw this very middle line (it is drawn through two points - the midpoints of equal sides), then you need to measure it, multiply the obtained value by two and add two lengths of equal sides.

## Polygon perimeter

To find the perimeter of a polygon, as a rule, the rule is to measure all sides and put them together. However, some special cases make it easier to cope with the task. For example, if you have a so-called regular hexagon in front of you, its perimeter can be calculated by multiplying the side length by 6.

## Circle perimeter

To calculate the perimeter of a circle or, as they say more often, the length of a circle, there is a special formula: P = 2πr, where π is a constant value equal to 3.14; r is the radius of the circle.The formula can also look like this: P = πd, where d is the diameter of a circle.

By the way, actually π is the ratio of the circumference of a circle to its diameter. It is proved that this value for all circles is the same and is 3.14.

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