Area of a Circle Formula and Problems with Solutions
Circle – Area – Formula and Problems with Solutions
Area of a circle is A = 𝝿r2
= 𝝿 (pi) x (radius)2 , where r is radius of the circle.
or when we know the diameter A = (𝝿/4) x D2
when we know circumference A = c2/4𝝿
Let us now solve problems on area of a circle.
Here are examples demonstrating the area of a circle with different radii.
Example 1: Small Circle
Radius (r): 3 cm
Area Calculation: A=πr2
A=π(3 cm)2
A=3.14×9 cm2A = 3.14
A=28.26cm2
- Draw a circle with a radius of 3 cm.
- Show the center (O) and the radius (r).
Example 2: Medium Circle
Radius (r): 5 cm
Area Calculation: A=πr2
A=π(5cm)2
A=3.14×25 cm2
A=78.5cm2
- Draw a circle with a radius of 5 cm.
- Show the center (O) and the radius (r).
Example 3: Medium Circle
The radius of a circle is 7 cm, what is the area of the circle.
Solution : Area of a circle is A = 𝝿r2
here radius of circle is 7 cm.
so, area of circle = 𝝿 x 72
= 3.14 x 7 x 7 cm2
Area of a circle is A = 153.86 cm2
Example 4: Large Circle
Radius (r): 8 cm
Area Calculation: A=πr2
A=π(8 cm)2
A=3.14×64 cm2
A=200.96cm2
- Draw a circle with a radius of 8 cm.
- Show the center (O) and the radius (r).
Summary of Areas:
- Circle with radius 3 cm: Area = 28.26 cm²
- Circle with radius 5 cm: Area = 78.5 cm²
- Circle with radius 8 cm: Area = 200.96 cm²
Example 5:
The radius of a circle is 30 cm, what is the area of the circle.
Solution : Area of a circle is A = 𝝿r2
here radius of circle is 30 cm.
so, area of circle = 𝝿 x 302
= 3.14 x 30 x 30 cm2
Area of a circle is A = 2826 cm2
Example 6:
Diameter of a circle is 9.8 cm, what is the area of the circle.
Solution : Diameter of a circle is 9.8 cm
Therefore, radius of circle = 9.8/2 cm
= 4.9 cm
Area of a circle is A = 𝝿r2
here radius of circle is 4.9 cm.
so, area of circle = 𝝿 x (4.9)2
= 3.14 x 4.9 x 4.9 cm2
Area of a circle is A = 75.46 cm2
Example 7:
In the figure two circles with same centre. The radius of larger circle is 8 cm, and radius of smaller circle is 4 cm.
(i)what is the area of the larger circle.
(ii)what is the area of the smaller circle.(iii)what is the area of the shaded part between two circles.
Solution : Area of a circle is A = 𝝿r2
here radius of larger circle is 8 cm.
so, area of larger circle = 𝝿 x 82
= 3.14 x 8 x 8 cm2 (i) Area of larger circle is = 200.96 cm2
now, radius of smaller circle is 4 cm.
so, area of smaller circle = 𝝿 x 42
= 3.14 x 4 x 4 cm2 (ii) Area of larger circle is = 50.24 cm2
(iii)The area of the shaded part between two circles
= 200.96 – 50.24 cm2
Area of shaded part = 150.72 cm2
Example 8:
Find the perimeter of the given figure, which is a semicircle including its diameter.
Solution : Diameter of given semicircle = 14 cm(5)
so, radius = 14/2
= 7 cm
According to the question
perimeter of figure = circumference of semicircle + diameter
= 𝝿r + D
= 22/7 x 7 + 14
= 22 + 14
perimeter of figure = 36 cm
By comparing these examples and their diagrams, we can see how the area of a circle increases with the radius. These visual aids help solidify the concept and make the math more engaging and understandable.