Before answering a question, sort out, than the circle differs from a circle. For this purpose do small work. At first draw a point in which place one leg of compasses with a needle on the sheet of paper. The second leg by means of a slate pencil put ends until they do not merge to one line – the closed curve. The circle turned out.
All end put by compasses which merged to the line are located on the plane. Each of these points is at identical distance from the central point in which there is a compasses needle. Now it is not difficult to give definition to a circle: it is the closed curve which all points are removed on identical distance from one, the circle called by the center. If to shade with a pencil that part of a leaf which is in a circle then we will receive a circle. A circle is called a part of the plane which is in a circle together with a circle.
Connect a piece any two points from among those which set in a set a compasses slate pencil. Such piece is called a chord. Let's draw a chord which will pass through the center of a circle. At last we approached the answer to the main issue. Diameter of a circle is called the straight line piece passing through its center and connecting two circle points which are most removed from each other. There will be correct also such definition: the chord which passes through the center of a circle is called radiuses. If AV – diameter of a circle, and R – its radius, then AV = 2R
As a circle – the closed curve, it is possible to calculate its length: With = 2πR where R is the radius already known to us. The number π is always constant and equal to 3.141592 … Now there is an opportunity to calculate diameter of a circle, knowing its length. For this purpose it is necessary to divide length of a circle into number π. Why to us all these calculations? This knowledge will be necessary for those who loves mathematics when they make more difficult calculations, for example, for the space industry. The others will be able easily and quickly to solve problems.