Pythagoras was a very brainy Greek gentleman who discovered loads of mathematical stuff, but the discovery most people know him for (and you need to learn!)is called Pythagoras' Theorem.
Basically, he discovered that if you stick squares onto the sides of any right-angled triangle the areas of the two smaller squares are equal to the area of the large one.
Or, to put it in technical terms, 'the square on the hypotenuse is equal to the sum of the squares on the other two sides.'
Now you just need to be able to use it!
Here's a few examples. The working shows each step needed to find the missing side. In each example, the missing side is called x:
First put the numbers into the formula:
Do the addition:
Now square root both sides to find x giving the answer to a sensible number of decimal places:
8.94 = x
So x = 8.94cm to two decimal places.
Here's another one where you are looking for one of the smaller sides, not the Hypotenuse!
As before, put the numbers into the formula:
Now subtract 4.42 from both sides:
Do the subtraction:
Square root both sides to find x:
x = 9.86cm to two decimal places.
Try this one yourself - type the length of the missing side into the space provided.