**Pi**(not pie) is usually attributed to Archimedes. In any case, it's been around for a

**long**time. And we use it in a lot of places (more on that later).

But first - what does pi represent?

In order to answer this question, I need to remind you about a tiny piece of geometry - about circles.

The measurement around the rim of a circle is called the

**circumference**. The measurement across the centre of the circle (from edge to edge) is called the**diameter**.Now at some point someone started investigating the

**relationship**between the circumference and the diameter of the circle. Something like I did (and you can do it too if you don't believe me), except they did it a lot more times and probably a lot more accurately.

Draw a circle using a compass or other circle drawer. Measure the circumference of the circle with a piece of string.

Measure the piece of string.

Calculate circumference divided by diameter (called the

**ratio**between circumference and diameter)
Repeat...

You see, if you do this accurately enough (which I definitely didn't) then you find that ratio is always

**the same**. In fact it's always roughly equal to**3,14159...**an irrational number which we call pi!
Now the first (and I think the most important use after all this fiddling around with string) of pi is to find the circumference of a circle more efficiently than measuring it with a piece of string!

Knowing just the diameter (or radius - half the diameter), we can use pi to calculate the

**circumference**!

*C = dπ = 2πr*And then we can also use pi to calculate the

**area**of a circle (you might notice that the circumference is the derivative of the area :-) )

*A=πr*^{2}^{Here are some alternative ways of writing pi. As you can imagine, each one is linked to a very special and mostly very advanced branch of Mathematics. Here are some super awesome everyday applications of pi.}

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^{That's all from me for today...we'll tackle e next time!}

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you could put a ~ on top of jj instead of dots and what would you get?

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