The word radius is transferred from Latin radius as ""a wheel needle, a beam"". Radius is called any piece of a straight line which connects the center of a circle or the sphere to any of the points lying on this circle or on the surface of this sphere as well length of this piece is radius. For designation of radius in calculations and mathematical expressions Latin letter R is used.
Instruction
1. Diameter of a circle represents a straight line piece which passes through the center of a circle and connects two points which are most removed among themselves lying on a circle. Length of this piece is called diameter of a circle too. Radius is equal to a half of diameter of a circle therefore if diameter of this circle is known to find its radius enough to halve it. R = D/2, where D – diameter of a circle.
2. Length of the curve forming a circle on the plane is circle length. In case circle length is known you can use a formula: R = L/2?, where L – circle length? – it is the constant equal 3.14159 … Constant? it is equal to the circle length relation to diameter, this size is identical to all circles.
3. The circle is the geometrical figure representing a part of the plane, limited to the curve being circle. If the area of a circle is known, then it is possible to find circle radius from the following formula: R = v (S/?) where v is a root square, S is the area of a circle.