Example: What is the area of a circle whose diameter is 10 cm?
Given: Diameter(d) = 10cm; So, Radius(r) = Diameter/2 = 10/2 = 5cm
Area of a circle: πr² = π x 5² = π x 25 = 25π sq cm

Example: What is the area of a circle whose radius is 5 cm?
Given: Radius(r) = 5 cm
Area of a circle: πr² = π x 5² = π x 25 = 25π sq cm

Example: What is the area of a circle whose diameter is 1 cm?
Given: Diameter(d) = 1cm; So, Radius(r) = Diameter/2 = 1/2 = 0.5cm
Area of a circle: πr² = π x 0.5² = π x 0.25 = 0.25π sq cm

Example: What is the area of a circle whose radius is 0.5 cm?
Given: Radius(r) = 0.5 cm
Area of a circle: πr² = π x 0.5² = π x 0.25 = 0.25π sq cm