AREAS RELATED TO CIRCLES

Introduction

* Circle: If 'r' is the radius and 'd' is the diameter of a circle, then

1. r = d/2

2. d = 2r

3. A = πr² (or) πd²/4

4. C = 2πr (or) πd

* Semicircle: If 'r' is the radius of a semicircle, then

1. P = r(2 + π) (or) 36r/7 (or) 18d/7

2. A = πr²/2 (or) πd²/8

* Quadrant of a circle: If 'r' is the radius of a quadrant of a circle, then

1. Area = πr²/4

* Sector: If 'r' is the radius 'θ' is the central angle (angle made by the

   corresponding arc at the centre) and 'l' being the length of the arc of

   a sector; then

 1. A = θ/360° × πr² (or) lr/2

 2. Length of arc = θ/180° × πr

* Segment: Ar(segment) = Ar(sector) - Ar (corresponding triangle.

* Concentric circles (Ring): If 'R' and 'r' are the radii of the bigger and smaller

           circles respectively, then

       A = π (R² - r²)