1. Area of Circle

2. Relationship between diameter and radius:
Diameter of a circle is twice of its radius.
Formula:
Diameter = 2 x radius
Radius = r O r A B d

3. Pi (π)
The ratio of circumference to diameter is constant for all circles. This ratio is called Pi and is written as π. Where π = C = π ⇒
C = πd ⇒
C = 2πr d 22 7

4. Area of a circle Area of the circle = πr² sq. units
The area of a circle is given by the formula
Area of the circle = πr² sq. units

5. Example 1: Find the area of a circle whose radius is 7 cm. Solution
Given:- radius(r) = 7 To Find :- area of circle
Area (A) = πr²
Divide 7 and 7 by 7
A = 22 x 7 = 154 cm

6. Example 2: Find the area of a circle whose diameter is 42 cm. Solution
Given:- Diameter =42cm To Find:- Area of circle
since radius(r) is not given we find radius(r) using diameter
Now we have found radius, Lets us now calculate area of circle
We know that Area = πr² 3
Divide 21 and 7 by 7
Area = 22 x 3 x 14 = 924 cm2 (Ans)

7. Try these Find the area of a circle whose diameter is 21 cm.
Find the area of the circle whose radius is 56 cm.