Circle call the closed curve which all points lie in one plane and are from the center equally spaced. There are also other definitions. The circle limits a part of the plane which is called a circle. These concepts need to be distinguished as the line and a geometrical figure have the properties.
surprisingpropertiesPeople paid attention to circle still in the ancient time. These properties became a basis for many geometrical calculations and architectural constructions. Practical application gave them an impetus to rapid development of a civilization, the principle of action of a wheel is based that all points of a circle are equally removed from its center. Faces need to build circles of people constantly. It is difficult to list all fields of activity in which it is necessary - design, construction, production of various details, design and many other things. In classical geometry the circle usually is under construction by means of compasses. This device invented in the ancient time allows to provide equal remoteness of all points from the center. Now in geometry and drawing use computer programs - for example, AutoCAD. This program allows to construct a circle, having set the radius and coordinates of the center or for three points. This opportunity is based on property that through three points which are not lying on one straight line it is possible to carry out only one circle. The equal remoteness of all points from the center provides also other properties of a circle. For example, it is possible to enter a regular polygon in a circle, and it will be only one polygon of a certain look. Its center coincides with circle radius, and distances from the center to tops are equal to radiuses. The regular polygon can and be described about a circle, and too only one. Its parties will be tangents, and respectively, to represent perpendiculars to radiuses. The circle around which the polygon is described is called entered, and about geometrical to a figure say that it is described. Parameters of a circle are connected among themselves. For example, length of a circle depends on its radius. It represents the doubled radius increased by constant coefficient of p, that is L=2pR. As the doubled radius is diameter, the formula of length of a circle can be transformed as L=pD. Respectively, radius or can be found, having divided circle length into the doubled p coefficient, and diameter - just on coefficient. The sizes of the corners connected with a circle also can be necessary for calculations. The corner can be central or entered. The top of the central corner is in the center of the circle. This corner makes 360º. If from a circle the arch is cut, then its central corner will depend on length of this arch. The top of the entered corner lies on a circle. The parties cross it this circle.