# How to calculate the perimeter?

## Watch the video

We often heard from teachers: "Do diligently, knowledge will be very useful to you in life", and, indeed, this happens. For example, when we undertake repairs, we absolutely need 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 forgot the school course, let's talk about how to calculate the perimeter of various figures.

## What is the perimeter?

The perimeter is the length of the line that delineatesgeometric figure; the length of all sides of a planar figure. Thus, to find the perimeter of a figure, it is enough to measure the length of each side and add up all the results. However, sometimes it can be done in a simpler way using special formulas. Next, we will analyze the ways of finding the perimeter of various figures using both methods.

## Perimeter of the triangle

Before calculating the perimeter of a triangle, it is necessary to measure the length of each side. After that just 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 result by two, and then add the length of the base to it.

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

## Perimeter of the quadrilateral

Let's analyze in this section how to calculate the perimeter of a square, rhombus, rectangle, parallelepiped and trapezoid.

### Square and diamond

As you know, the square has four sides and all of themare equal, and therefore, to calculate the perimeter of the square, you need to measure one of its sides, and then multiply the obtained value by 4. Strictly speaking, the perimeter of the diamond is exactly the same, because in rhombus all sides are equal.

### Rectangle and parallelogram

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

### Trapezium

Trapezium is another type of quadrangle. This figure, as a rule, has all the sides of different length, and therefore to find the perimeter it is necessary to measure each side and fold them. However, the trapezoid can be isosceles. In this case, the following formula can be used to calculate the perimeter: P = a + b + 2c, where c is the length of one of the equal sides.

By the way, there is another way of determiningperimeter of an isosceles trapezoid - the so-called "midline method". First you need to draw this very middle line (it is drawn through two points - the middle of equal sides), then you need to measure it, multiply the result by two and add two lengths of equal sides.

## Perimeter of the polygon

To find the perimeter of a polygon, bothrule, the rule is - measure all the parties and fold them. However, some particular 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.

## Perimeter of the circle

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

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