The perimeter is the sum of lengths of the parties of any geometrical figure. In other words, if to take thread and to lay out with its help on a table, for example, a square, and then to measure length of this thread, then the received figure also will be perimeter of this square. All know what is perimeter, but not everyone can think at once as to calculate it. For measurement of perimeter of different figures there are various ways.

## Instruction

1. Square. It is well-known that the square has 4 parties and they are equal. Therefore the formula for calculation of its perimeter looks so: P=4a where and is the length of one party of this figure. In other words, measure one of the parties of a square and increase this figure by the number of the parties, that is on 4. The perimeter is equal in our case to 16 cm (4*4).

2. Rectangle and rhombus. At these two figures only the parties parallel each other are equal, respectively the perimeter is defined as follows: É = (and +b), where and and b – the adjoining parties. Thus, on our example the perimeter of a rectangle is equal to 24 cm (2*(8+4)).

3. Triangle. As triangles are absolutely different – isosceles, wrong, with right angles, the only certain way to define perimeter of such figure the formula is: É =. That is for calculation of perimeter of a triangle just measure lengths of all three parties and put the received figures. The perimeter of a triangle is equal in our case to 10.7 cm (2+5+3.7).

4. a circle call length of a circle which is calculated on a special formula: É =, where d is the diameter of a circle, and is 3.14 a number "пи" which is specially removed by scientists for determination of perimeter of this geometrical figure. Our circle (see the drawing) has in the diameter of 3 cm, that is the perimeter of a circle is equal to 9.42 cm (3*3.14).