Instruction

1

A circle is a curve bounding a plane, called the circle. In other words, the circumference is called the locus of points in the plane equidistant from the centre. Segments connected to a center

**of a circle**are called its radii, and the distance from one point to another passing through the centre is called a diameter**of the circle**. The diameter**of a circle**equal to twice the radius: D=2r. The equation**of a circle**in analytic geometry is:x^2+y^2=R^2Существует also the concept of the chord**of the circle**. It is also obtained by connecting two points**of the circle**, but not necessarily passes through its center. All the diameters that pass through the middle of the chord perpendicular to it. The biggest chord**of a circle**is its diameter.2

As with any curve, a circle has a certain

*length*p. It has long been observed that the length**of a circle**relates to its diameter the number PI:p/d=patsada it follows that p=πd, or p = 2nr, where r is the radius**of the circle**.The number π is an irrational value, but it is approximately equal to 3.14.Knowing*the length***of the circumference**, and determine the area of the ring bounded by two circles. It is equal to:S=2nr*k, where k is the distance between the inner and outer circumferences of the ring; 2nr - length internal**circumference**of the ring.3

Graphical way to determine the length of

**the circumference**, because of its inaccuracies, is rarely used. For this purpose an odometer is a device for measuring the length of a curve. Anywhere**circles**mark the start point of the measurement. To bring her odometer, and lead him along the line until it gets to the same point.4

The definition of the length

**of the circumference**has considerable practical value. In addition to mathematicians, it is necessary to carry out physicists, astronomers. First calculate*the length***of the circumference**of elementary particles, the second of the heavenly bodies. Also, knowing the diameter of the circus arena, a running track, guided by the above formulas, we can calculate what distance they will run a horse or runner at a range.