The circumference is one of the simplest and basic geometric figures that we know of. We could define a circle as the figure generated by a closed curve or perimeter in which there are no vertices or internal angles. In addition, the circumference does not have differentiated sides, as it does with other figures such as the square or the triangle.
To define the circumference, we can start by paying attention to the etymological meaning of the word, which in Latin means 'to carry around'. The circumference can normally be confused with the circle, but if we speak correctly, we must say that this is the internal surface of a circle, while this is its perimeter.
The circumference is always two-dimensional and has a radius, which is the distance between the points found (which mark the limit of the figure) to the center of it. In addition, other elements that make up the circumference are the center (the point equidistant from all the other points in the figure), the diameter (the distance between the two furthest points that pass through the center), the chord (any segment that one two points of the circumference), the secant and tangent lines (the first being the one that passes through the inside and outside of the figure, dividing it into two sectors; the second being the line that passes outside and touches the circumference in a just point).
As for the angles of a circle, these can be central, inscribed, semi-inscribed, interior and exterior. In addition, different relationships can also be established in the presence of two or more circles. This is where we must talk about exterior circumferences (those that do not share common points), exterior or interior tangents (those that share only one common point, a shared point on the outside or inside respectively), secants (which are divided into two segments each one by the intersection generated by both), eccentric and concentric interiors (whether or not they have the same center). Finally, the coincident circles are those that have the same center and radius, and that converge in a single figure.
