Length of the circle is, in fact, its perimeter, i.e. the sum of the lengths of all sides. But since the concept of "party" does not apply to the circumference (it represents one single curve, all points of which are equidistant from the center), is calculated exactly the length of the entire figure.
This value is denoted as, which is called the whole circle and marked the center. For its size it is necessary to know what the circumference of the radius (R) or diameter (D=2R). The diameter of the circlemultiplied by PI, resulting in the desired length of the circumference. The same result gives that same number multiplied by two and the magnitude of the radius (since radius is half the diameter).
The number "PI" has a lot of figures in your composition. What we do for calculation is required, its value, rounded to hundredths of parts is 3.14.
The result of the calculation is written in centimeters or in those quantities, which have given the radius or diameter.
If you need to find the length not the entire circumference, but only its part, for the calculations we need, in addition to the radius, the measure of an angle whose apex is at the center of the circle, and the parties to limit the measured arc (this argument is given in radians). To find the length of an arc, multiply by the radius.