Pythagoras

Pythagoras is quite famous because of his rule about right-angled triangles. If you know the length of two sides you can work out the third. Let's call the hypotenuse 'h', the adjacent 'a', and the opposite 'o'. Don't be confused by the adjacent and the opposite and which is which. You can recognise the hypotenuse so you only have two sides to consider. If you are given an angle then you know which is the adjacent. if you aren't given an angle then just choose one i.e. just label the sides 'a' and 'o'. As long as you know which is which then that is the important thing.

Pythagoras said hxh = axa + oxo. Usually you hear this rule as 'the square of the hypotenuse is equal to the sum of the square of the other two sides'. It is well worth learning this phrase, but the main thing to know is that the longest side squared is equal to one side squared plus the other side squared.

One very common right-angled triangle that you will come across is one with lengths 3,4 and 5. This is because 3x3 + 4x4 = 5x5. In other words 9+16 = 25. Do look out for 3,4, 5 triangles.

That sums it up