BBIS: Circles

• Mathematics
• Lower Secondary (Key Stage 3)

Circles

Area of circles

How do we find the area of a circle?

Area Of A Circle

Here we will learn about calculating the area of a circle including how to calculate the area of a circle given the radius, how to calculate the area of a circle given the diameter and how to calculate the area of a circle given the circumference.

What is the area of a circle?

The area of a circle is given by the area of a circle formula which is made by using a specific relationship between the radius of a circle and its area.

Area of a circle formula:

π × r × r

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What is pi? π

π (pronounced pi) represents the ratio of the circumference of a circle to its diameter. 

For all circles if you divide the length of the circumference by the length of the diameter you get the value π

π is an irrational number which means it cannot be written as a fraction. It is a non recurring decimal and has an approximate value of 3.14159

Alternatively you can use the value 3.142

Sometimes a question may ask you to leave an answer in terms of pi

E.g 6 × π = 6 π

6 × π = 6 π (this is an answer in terms of pi)

8 × π = 8 π

8 × π = 8 π (this is an answer in terms of pi)

10 × π =  31.41

10 × π = 31.41 (this is an answer not in terms of pi)

Area of a circle