# Circle

## Definition of a Circle

The Circle is a collection of all the points in a plane, which are at a fixed distance from a fixed point in the same plane.

## Euclid’s Definition of Circle

A circle is a plane figure bounded by one curved line, and such that all straight lines drawn from a certain point within it to the bounding line are equal. The bounding line is called circumference and the point is called the centre.

The figure indicates the depiction of a circle. In the circle as shown in the figure, the fixed point $O$ is called the centre of the circle.

## Radius of a Circle

The distance from any point on a circle to the centre is called radius of the circle. The radius of a circle is represented by the letter $r$.

In the figure, the radius of the given circle is denoted by the line $OP$, drawn from the point $P$ on circle to the centre $O$. There are infinite number of points present in a circle. Therefore, for a given circle, an infinite number of radii can be drawn and all the radii are of equal length.

## Chord of a Circle

The chord of a circle can be defined as the straight line that connects any two points in the circle. For a given circle, there is an infinite number of Chords. In the figure, the straight line $RS$ drawn from the point $R$ to $S$ is a chord of the circle.