# Maths - Get a piece of the pi

On Thursday 14 March at 1.59pm precisely, I will be hosting a free online event to celebrate one of the most ubiquitous and enigmatic numbers in maths: pi.

The number defines the ratio of the circumference of a circle to its diameter. So if a circle is one metre across then the number of metres it takes to go round the outside of the circle is 3.14159... And then the numbers spiral off to infinity in a dizzying dance of digits. It is these digits that define the date for our celebration of pi. The first digit gives you the month: 3 for March. The next two digits give you the date: 14. The next digits give you the time that celebrations kick off, hence 1.59pm.

The event is being organised by the new Oxford Connect initiative run by the Department for Continuing Education at the University of Oxford.

Calculating a value for pi has obsessed mathematicians since ancient times. The Rhind Papyrus written by the Egyptian scribe Ahmes in about 1650BC approximates pi as 25681 or roughly 3.16. Not bad for a first estimate. As maths developed, more cultures had a go at capturing this important number. The ancient Greek mathematician Archimedes used a 96-sided shape to estimate that pi lay between 22371 and 227. This is where we get the approximation that most engineers use for pi of 227. In fact, engineers celebrate Pi Day on 22 July.

During the hour-long event I will be introducing a range of weird and wonderful ways to calculate pi, which participants will be encouraged to try. My favourite is Buffon's Needle, which involves taking a box of matches and drawing a series of parallel lines at a distance of two matchsticks in length apart. You then toss the matches down and count the number of matches that cross the lines. Mathematical analysis reveals that if you take the total number of matches tossed and divide by the number that cross the lines then the answer should be close to pi. So by collecting the data from enough tosses we should be able to get an estimate for pi.

I hope as many people as possible will join us online in our interactive experiment to rediscover the joy of pi.

Visit oxfordconnect.conted.ox.ac.uk to find out more. Look out for an interview with Marcus du Sautoy, professor of maths at the University of Oxford, in TES on 29 March.

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