How to calculate the area of a Circle: C=πr2

But what does this mean?

Some facts you might need to know first:

circle is a shape where every point on its edge is the same distance from the centre.

The distance from the centre to the edge of the circle is called the Radius.

The distance from one side of the circle to the other, going through the centre, is called the Diameter. This is also double the length of the Radius.

π (pronounced Pi) is a special number that is calculated by dividing the circumference of a circle by the diameter. No matter what size circle you have, this number always stays the same. In reality, this number is never ending, but we can approximate it to 3.14, but to make it easier for us, since this number never changes, we just call it Pi and write it π.

The Area of a circle

C = circumference
d = diameter
r = radius

The formula for an area circle, if you know its radius, is given by:

A= π r2

But what if you know the diameter?

You can either divide the diameter by 2 which gives you the radius and then use the formula above or use:

A=(1/4) x πd2

Remember, the area of a circle is given in square units! (e.g cm2)

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