Pythagoras determined that when three squares are arranged so that they form a right angle triangle, the largest of the three squares must have the same area as the other two squares combined. In the picture below, you can see how the sum of the squares creates the right triangle ABC.
This realization about the area of the squares led to the Pythagoras theorem:
This theorem is an extremely useful tool that provides the basis for more complex trigonometry theories such as the converse of the Pythagorean theorem.
The discovery of Pythagoras' theorem led the Greeks to prove the existence of numbers that could not be expressed as rational numbers. For example, taking the two shorter sides of a right triangle to be 1 and 1, we are led to a hypotenuse of length , which is not a rational number.
