When a line AB rotate by 360 degree taking center A, thus obtained figure is called circle.

A is called center of circle. A to any point on the circle joining is called radius, a line passing through the center of the circle is called diameter of circle and its value is 2 * radius.

The ratio between circumference to diameter is always constant and denoted by its value is or 3.14 approximately.

so circumference of circle (p)=

Area of circle=

=

We divide a circle in to many small sectors, thus the length of an arc is reached near about the length of chord. Then merge them as below we have obtained a ractangle.

**length of Chord**

Length of chord=

where 2a=lengh of chord

h= height of arc

r=radius of circle

length of arc= arc/oce=Angle in degree/360

Radion: If are is equal in length to the radious, then the angle for form are called radion.

**Segment of a circle** – chord AB of a circle divides the circular region into two part, each part is called a segment of the circle.

**Sector of the circle**– the area surrounded by an arc and the two radius joining the end point of the arc with the center is called a sector of the circle.

**Concentric circle**– two or more circles with the given centre are called concentric circle.