For starters, understand the terms and definitions with which you have to work with. Note that a circle is a figure consisting of all points in the plane, for each of which the ratio of distances to two given points is equal to this number, different from unity. Radius is not only the value of the distance, but the segment that connects the center of the circle with one of its points. The circumference is the value of the segment AB consists of points A, b, and all points in the plane from which the segment AB is seen under a right angle from the diameter. PI is an irrational number, then there is a never ending and non-periodic and which is the length of the semicircle, the radius of which is equal to one, the number PI is approximately equal to 3.14.
So, according to the first method, to calculate the radius of the circle is possible, if you know the radius of the circle. To do this, multiply the length of the radius by PI, approximately equal to 3.14, and in figure 2. In other words, the standard formula calculation of the radius of the circle is: L = 2 x P x R, where L is the circumference, N is the number PI (~3,141592654), R is the radius of the circle. It should be noted that from this formula we can calculate, what is the radius: R = L / (2 x P).
There is a shorter formula to find the circumference. The formula is: L = R x alpha, where L is the length of the arc, R is the radius of the circle, alpha is the angle of the arc in radians. A circle is nothing but a closed arc whose angle is 2 x PI radians, so theoretically we again get a formula for the length of the circle L = 2 x PI x R, which indicates the correctness of the formula. It also follows that the number of alpha is also a constant value and is 2 x PI = 6.28 to. Thus, to find the circumference, multiply the radius of this circle is the number of 6.28.