Area of Circle

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

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

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

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

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)

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