π  Where did it come from?
No one really knows how Pi was discovered; mathematicians have known the number for over 4000 years though! Euclid who was a Greek mathematician, born in 325 BC, was responsible for Euclidean geometry and this was the first recorded system used to show Pi as a mathematical constant.
William Jones first used the Greek symbol ‘π’ in 1706 when he published his book: A New Introduction to Mathematics. This notation became standard after it was adopted by Leonhard Euler in 1737.
An approximation of Pi is 3.14159.
It was Aryabhatt in the fifth century who used the approximation 22/7 as the constant in the calculation to measure the earth’s circumference.
Pi has now been evaluated to over a trillion decimal places by computer!
Check out this website to see one million digits of Pi! http://www.piday.org/million/
Remember Pi to 30 decimal places…
Impress everyone at your Pi Party and write Pi to 30 decimal places using this neat trick provided by our fantastic tutor manager, Mark, at the CAMI Tutor centre!
Memorise the following nonsense rhyme:
Sir, I sent a rhyme excelling
In sacred truth and rigid spelling
Numerical sprites elucidate
For me the lexicon’s dull weight
If nature gain not you complain
And Dr Johnson fulminate
The number of letters in each word represents a digit of Pi:
Sir, 
I 
sent 
a 
rhyme 
excelling 
3. 
1 
4 
1 
5 
9 
In 
sacred 
truth 
and 
rigid 
spelling 
2 
6 
5 
3 
5 
8 
Numerical 
sprites 
elucidate 

9 
7 
9 

For 
me 
the 
lexicon’s 
dull 
weight 
3 
2 
3 
8 
4 
6 
If 
nature 
gain 
not 
you 
complain 
2 
6 
4 
3 
3 
8 
And 
Dr 
Johnson 
fulminate 


3 
2 
7 
9 
3.141592653589793238462643383279
To look extra impressive you can even look up further digits of Pi and make up more lines to the poem!
So, now you know a little about the history of Pi and a cool trick, it’s time to get serious before you learn how to party for Pi!
What do we use Pi for?
For any circle, circumference ÷ diameter = 3.141592....... (π)
You can’t work out an exact value of π (remember it has over a trillion digits and counting!), so approximations are used. These include 3.14, 3.142 and ^{22}/_{7}.
All scientific calculators have a π button. You can use this to make your calculations more accurate.
If no calculator is available, or an approximate answer to a calculation involving π is required, then round π to 3 (or whatever is suggested).
Circumference
Circumference is the length of the edge all the way around a circle.
We know that circumference ÷ diameter = π
Therefore, circumference = π × diameter.
This can be shown in the following formula:
C = π d
The diameter is twice the length of the radius. This formula can be written as:
C = 2 π r
So if, a circle has a diameter of 10cm. Find the length of its circumference. (Use π = 3.14)
Using C =πd
C = 3.14 × 10
C = 31.4 cm
Using C = 2 πr
C = 2 × 3.14 × 5
C = 31.4cm
Area
Area is the space inside a circle.
This is the formula for the area of a circle:
A = π r²
πr^{2} means π × r × r.
Be careful with this as only the 'r' is squared, not Pi.
Example 1
Find the area of a circle of radius 6cm
r = 6cm, so we calculate A = 3.14 × 6 × 6 = 113.04cm^{2 }
Example 2
Find the area a circle of diameter 10cm
The diameter is 10cm, so the radius is 5cm. We calculate A = 3.14 × 5 × 5 = 78.5cm^{2}
^{ }
When calculating the area of a circle, remember to use the radius, not the diameter.
A Pi Party?! When?!!
Pi Day is celebrated on March 14^{th}. (3/14! à 3.14!)
This is also Albert Einstein’s birthday (1879)!
You may have missed National Pi Day this year, however you can celebrate Pi on the 22^{nd} of July as well! 22/7!
Some Top Tips for Pi celebrations
 Eat Pi foods!
There are lots of ways to do this. Obviously you should start with pies! Meat pies, vegetable pies, fruit pies, lemon meringue pies, key lime pies!
You can also drink and eat food that has the word ‘pi’ within it: pizza, pineapple, pine nuts…
 Create a Pi Party atmosphere!
Wear a Pi Tshirt, Pi jewellery, use a Pi mug…
Change your computer wallpaper to something Pi related!
Play music that reminds you of Pi e.g. American Pie. You can also listen to Kate Bush. She performed a song called ‘π’ on her 2005 album, Aerial, in which she sings Pi to its 137^{th} decimal place (well, excluding the 79^{th} to the 100^{th} decimal digits! No one knows why!)
Make Pi decorations – balloons with ‘π’ on them and digits from Pi!
 Play Pi games!
Get a piñata! Have a pie eating contest, answer Maths questions, design Pi posters, find the most creative way to write Pi or contests to see who can recite the most digits of Pi (see above for this cool party trick!)
 Go for a Pi mile run (or walk)!
You can do this with family and/or friends and even raise money for charity.
 Keep celebrating Pi every year – on March 14^{th} and 22/7 if you are very dedicated!