**Important Concepts and Formulas**

1. The Greek letter Ï€
is defined as the ratio of the circumference to the diameter.

Circumference = Ï€ × diameter

= Ï€ × 2r (where r is the radius
of the circle)

= 2Ï€r

2. The area of a circle = Ï€r

^{2}
To know the formulas for areas of different 2D shapes
-------- Click Here!

3. The length of an arc of a sector of a
circle with radius r and with central angle Î¸ is given by:

4. Area
of a sector of a circle with radius r and with central angle Î¸ is given by:

5. Area
of segment of a circle = Area of the corresponding circle – Area of the
corresponding triangle.