A circle is a closed curve. The points that lie in its plane, equidistant from the centre, which lies in one plane together with a curve. Radius - a segment of a circleconnecting its center with any point. With its help, you can learn many other parameters of the figure, so it is a key parameter. The numerical value of the radius will be the length of this segment.
You should also distinguish the radius of the shape from its diameter (diameter connects the two most remote from each other point). To use a mathematical method of finding the radius you need to know the length or diameter of the circle. In the first case the formula will look like R = L/2?", where L is the known length of the circumference, and the number ? equal to 3.14 and is used to denote a particular irrational number.
In the case that the only known diameter, the formula will look like R = D/2".
If the length of the circle is unknown, but there are data on the length and height of a segment, the formula would be R = (h^2*4 + L^2)/8*h where h is the height of the segment is the distance from mid-chord to the most protruding part of the said arc) and L is the length of the segment (which is not the chord length).Chord – a line segment that connects two points of a circle.
It is necessary to distinguish the concept of "circumference" and "circle". The circle is part of the plane, which, in turn, is limited by the circumference of a certain radius. To find the radius, you must know the area of a circle. In this case, the equation would be R = (S/π)^1/2, where S is a square. To calculate the area, in turn, should know the radius (S = NR^2").