Pythagoras’ Theorem states that ‘the square on the hypotenuse is equal to the sum of the squares on the two shorter sides’. Of course, it only applies to right-angled triangles, but is a very important theorem. It can also be used in reverse, to check if an angle is 90^{o}. See how well you remember it in this Maths GCSE quiz!

Although Pythagoras didn’t discover the relationship between the length of sides in a right-angled triangle (the Babylonians knew this 1,000 years earlier) he was possibly the first to prove it, over 2,500 years ago. Pythagoras was more than just a mathematician – he founded a school that studied philosophy and religion, and was head of the Secret Pythagorean Society.

[readmore]

The inner circle of members were not allowed personal possessions, had to be vegetarian and follow strict rules. The Society was based on the belief that everything in the world could be written as a relationship between the Natural numbers (See the *Numbers Classification* quiz if you don’t know what these are), but it all fell apart when it was discovered that √2 is irrational. Members of the Society tried to keep it a secret, but a whistleblower revealed the secret, and the Society collapsed. All that because of a number!

Fortunately for us, Pythagoras’ best known result didn’t collapse along with his Society, and its use is widespread, from geometry to algebra, from house-building to space exploration.

[/readmore]