A circle is understood to be that geometric figure that consists of a shape established from a closed curved line. The circle has a main characteristic that is that all the points that are established from its center have the same distance towards the line that serves as the perimeter, that is, they are equidistant. An important clarification in terms of what a circle represents is one that shows us that the circle is the surface of the plane inside a circumference. Thus, the circumference is the limit or the perimeter of the circle, a limit established by a closed curved line. Therefore, both terms should not be confused or taken for the same, although in common language this error is usually made.
The circle is one of the most basic geometric figures around which other figures are built, for example the cone. It is the only one that does not have any straight line as a determining factor and therefore the angles that can be established within it necessarily require the marking of imaginary internal straight lines. In the circle, as in the circumference, there are therefore no vertices.
There are several concepts that are important when analyzing or defining the specific characteristics of each circle. In this sense, we must always speak of radio when we speak of a circle. The radius is the segment that is established between the center of the circle and any of the points on the circumference. In order for us to speak of a circle proper, all the segments that we establish between the radius and the circumference must have the same length, that is, they must be equidistant from the radius and the circumference or perimeter.
Another important concept is that of diameter. The diameter is the length of the circle if we draw a segment from one point to another point on the circumference, always passing through the center. By always having to be the same length, regardless of where we draw the diameter, this segment should, as a result, allow us to divide the circle into two parts of equal size or surface. The diameter, in short, is the union of two spokes. Finally, if we mark two different radii, perpendicular to the circle and extend them to the circumference, the distance that is marked on it between one and the other is known as the arc. The arc does not pass through the center of the circle. The chord is a segment that joins two points on the circumference without touching the center.
