In Ancient Greece there was a man called 'Pythagoras.' He made really imporatant developments to maths. One of these is a theorem about triangles. Right-angled triangles to be exact. He worked out a little gimmick to work out the length of any side. Let's start with the hypotenuse.

All you need is the length of two sides. In order to work out the length of the hypotenuse we need to use an algebraic method. First of all the formula. (A x A) + (B x B)= (C x C) with C being the length of the hypotenuse. Then you find of the square root of the answer of the equation and you have worked out the side length.

Now let's put this into practice. Two of the known side lengths are 3 and 4. We are working out the length of the hypotenuse. So first we square the known lengths. Now we have 9+16=C. The answer to this is obviously 25. The square root of 25 is 5. Therefore the length of the hypotenuse is 5.

You can use this theory to work out other side lengths. All you do is re-arrange the equation so the missing side length is the subject. Eg: 9+ ( b x b) =25
-9
(b x b)=25-9
25-9=16
4(insert unit of measurement here.)

If they ask you to do this on a triangle type other than a right angle in an exam to work out a side length don't panic. All you do is draw a line down the middle of the triangle so that it is split into two equal halves. Re-arrange the equation to find the side and then you work it out. Remember to square root the answer. If it is asking for the bottom side length then you must times the square root by two.