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# what is pi?

By henry warren on the 25th of January, 2013

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It's an infinite number but at this level you can consider it to be 3.142

Some people take great pride in being able to recite pi up to a huge number of decimal places. The current record holder is a Chinese guy called Chao Lu who can recite it up to 67,890 places. Which is impressive but also remarkably pointless.

By henry warren on the 25th of January, 2013

## Calculate the circumference of a circle

Equation for the circumference of a Circle: C=2πr

But what does this mean and how did we get this?

Some facts you might need to know first:

A 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 circumference of a circle is just another way of saying the perimeter of a circle, the distance around the edge of a circle.

The Circumference of a circle

C = circumference
D = diameter

If π is calculated by the circumference of a circle diving by the diameter we can rearrange this to work out the circumference.

π = C/d

We multiply both sides of the equation by d to get:

π x d = C

We rewrite this to make it look nicer as simply:

C=πd

Alternatively, since the diameter is twice the radius, we can rewrite this in terms of the radius, but either way is correct!

C=2πr

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