What is Pythagoras' theorem?

Pythagoras' Theorem is a rule for right-angled triangles which is used to solve problems.

Explanation:

For any right-angled triangle, the longest side (opposite the right angle) is called the hypotenuse. If you square the length of the hypotenuse, this will always be equal to the sum of the squares of the other two lengths. This is Pythagoras' Theorem. 

Example: if the hypotenuse is 5cm long, and the other two lengths are 3cm and 4cm long...

55 = 44 +3*3

25 = 16 + 9

25cm = 25cm

This rule can be used to work out missing lengths. If one of the above lengths had been missing, you could have used the equation to calculate the missing length:

a^2 + b^2 = c^2

where c is the hypotenuse and a and b are the other two lengths.