The **elements of the circle** They correspond to several lines and points that can be drawn inside and around its perimeter for the measurement and verification of certain geometric properties.

These elements are the center, radius, diameter, chord, secant line, tangent line, and arc. A circle is a closed curved line that is equidistant from a center, so all points are the same distance from it.

It is usual to confuse the concepts of circumference and circle, the first being a curved line and the second the surface enclosed by the circumference.

**Basic elements of the circumference**

Usually in the study of basic geometry you work a lot with circumferences and circles, since these allow you to make several simple measurements.

In addition, the demonstration of several of its elementary properties are useful to develop cognitive abilities.

**1- Center**

It is the midpoint of the circle, located literally in the center of the figure at an equidistant distance from all the other points on the drawn line that makes up the circle.

On the center of a circle infinite lines can be drawn that allow defining its properties and delimiting segments to carry out measurements of length, angles or equivalences.

**2- Radius**

Any straight line that joins a point on the circumference with its center will be called radius, the basic element of any circle and circumference, since it is used to calculate other magnitudes such as the surface.

Although infinite lines can be drawn between a circle and its center, they will all always have the same length.

The calculation of the radius of a circle corresponds to its perimeter divided by 2 pi (radius = perimeter / 2π), it is equivalent to half the diameter.

**3- Diameter**

It is a segment that joins 2 points of the circumference passing through its center. The diameter is then a *middle line* that divides a circle into equal parts.

There can be infinitely many lines in diameter, but they will always measure the same. The value of the diameter of a circle is equal to twice the radius.

**4- Rope**

It is a line that joins any 2 points of a circumference and is not subject to any condition (as is the case of the diameter). Within a circle there can be infinite chords.

**5- Secant line**

A secant line is a line that *divide* a circle at 2 points. Unlike the radius, the diameter or the chord, which only touch the circumference, a secant line crosses it beyond its limits “cutting” it. In fact, the word secant comes from the Latin *I will dry*which means to cut.

**6- Tangent line**

A line that, being perpendicular to the radius, touches the circumference at a single point, is a tangent line.

This type of line is located on the outside of the circle and can have a variable length, although it is usually not greater than the diameter of the circle itself.

**7- Arch**

It is the segment of a circle product of the path of a chord. An arc is made up of 3 points: the center and the 2 places where the chord touches the circumference.

**References**

Paul Dawkins (sf). Calculus I: Tangent Lines. Retrieved on December 10, 2017, from Math Lamar.

Concept of circumference and its elements (sf). Retrieved on December 10, 2017, from Cecyt.

Circle (nd). Retrieved on December 10, 2017, from TutorVista.

Circumference (sf). Retrieved on December 10, 2017, from Math Goodies.

Radius, diameter, & circumference (sf). Retrieved on December 10, 2017, from Khan Academy.

Arc (nd). Retrieved on December 10, 2017, from Math Open Reference.