Area of circle and polygons 
1. Circumference
The segments that join the center with the circumference points are called radius.
The segment passing through the center and connects two points on the circumference is called diameter. It is equivalent to two radiuses.


If we have a coin and we paint its edge, when we move it through a paper, it will leave a mark. The length of that mark is three times the length of the diameter and a little more.
If the circumference of the coin is 44 cm and the diameter is 14.012738 cm, we find that 44:14.012738 = 3.14. Therefore the diameter fits three times in the circumference and there is an excess: 0.14. The number 3.14 is called p
(pi).
Circumference = 3.14 x length of its diameter. As the diameter is equal to two radius, we can also say that the length of the circumference = pi x 2r = 2 pi
x r. p x 2r = 2
p r.
Example: If the diameter of a circumference is 16 cm, its length will be: 3.14 x 16 = 50.24 cm.
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