Circle Math

In circle math the terms related to the circle are discussed here.

A circle is such a closed curve whose every point is equidistant from a fixed point called its center.

The symbol of circle is O.

Symbol of Circle

What are the terms related to the circle?

The terms related to the circle math are:

(i) Center:

The center of a circle is a fixed point within the circle from which all the points of the closing curve are equidistant.

Centre of a Circle

O is the centre.

(ii) Circumference:

The curve which closes a circle is called its circumference. The length of the circumference is called the length of the circle.

Circumference of a Circle

(iii) Radius:

The distance from the centre to any point on the circumference of a circle is called the radius of the circle. The symbol of the radius is r.

Radius of a Circle

(iv) Diameter:

The line-segment passing through the centre and meeting the points on the circumference is called the diameter of the circle. Diameter is denoted by 'D'.

Diameter of a Circle

AB is a diameter of the circle.

Diameter is twice the length of the radius concerned.

Thus, D = 2r [Diameter = 2radius]


r = D/2 [Radius = Diameter/2]

(v) Arc:

Any part of the circumference is called an arc of the circle.

Arc of a Circle

(vi) Chord:

The line-segment joining the two ends of an arc is known as a chord. A diameter is the longest chord of a circle.

Chord of a Circle


O is the centre.

OP is one radius.

AB is a diameter.

MN is a chord . (line-segment)

OA and OB are also radii.

Related Concepts on Geometry - Simple Shapes & Circle

Simple Closed Curves


Different Types of Polygons




Circle Math

Line Symmetry

Symmetrical Shapes

4th Grade Math Activities

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