Pythagoras' Theorem relates the lengths of the sides in a rightangled triangle.
A rightangled triangle has one angle of 90°. The side opposite the right angle is always the longest side, and is called the hypotenuse.
The diagram on the left shows a rightangled triangle. 
Now look at the diagram on the right. A square has been drawn on each of the sides of the triangle above. We are going to examine the areas of each of the squares.
Shorter sides
Hypotenuse
How they are related

Pythagoras' Theorem Pythagoras' theorem states that if you square the two shorter sides in a rightangled triangle and add them together, you get the same as when you square the longest side (the hypotenuse).

Practice Questions
Check if the following triangles are rightangled. They are not drawn to scale, so you can't tell by just looking at them.
Work out the answer to each of the questions below then click the
button to see whether you are correct.
