Pythagoras's Theorem is used in a right-angled triangle, the side opposite the right angle is called the hypotenuse. It is the longest one in the three sides.
The formula of Pythagoras's Theorem is the area of the square placed on the hypotenuse of a right-angled triangle is equal to the sum of the areas of the squares on the other two sides.
However Pythagoras is not the first person who discovered this theorem. For more information, go to earlier Pythagoras' Theorem
