Determination of radius of a circle is one of the main objectives of mathematics. There is a set of formulas for accounting of radius, it is enough to know some standard parameters only. Graphically radius is designated by means of letter R of the Latin alphabet.

## Instruction

1. A circle is the closed curve. The points which are in its plane are equidistanted from the center which lies in one plane together with a curve. Radius - the circle piece connecting it the center to any its point. With its help it is possible to learn many other parameters of a figure therefore it is key parameter. Numerical value of radius will be length of this piece.

2. Also it is necessary to distinguish figure radius from its diameter (diameter connects two points which are most removed from each other). To use a mathematical way of finding of radius it is necessary to know length or diameter of a circle. In the first case the formula will look how "R = L/2?", where L is the known length of a circle, and number? equally 3.14 it is also applied to designation of a certain irrational number.

3. In case only diameter is known, then the formula will look as "R = D/2".

4. If length of a circle is unknown, but there are data on length and height of a certain segment, then the formula will have an appearance "R = (h^2*4 + L^2) / 8*h" where h – the segment height (is distance from the middle of a chord to the most acting part of the specified arch), and L – segment length (which is not chord length). A chord – a piece of the line which connects two points of a circle.