To understand the circle considers the two dimensions -Plane. The set of all points in a plane which are equidistant from some fixed point in the plane is called a circle. The fixed point is called the centre of the circle. The fixed distance from the centre to the points of the circle is called the radius of the circle. If we draw a curve, keeping in mind the definition of circle, the curve in the diagram will be drawn. This is a circle. With centre is represented by and radius is denoted by .
If and are the centre and radius of the circle respectively, then the set of the form is a circle, where is any point of the circle. By this notation it represents the distance between point and centre is equal to the radius.