Pythagoras' Theorem animation showing the squares of the sides of a right angled triangle. Pythagoras' Theorem relates the lengths of the sides of a right-angled triangle and says that the square of the length of the hypotenuse (the side opposite the right angle, green) equals the sum of the squares of the other two sides (pale blue and pink). This animation shows the hypotenuse rotating about its left point and so creating a smoothly changing right-angled triangle. The other two sides are extended to form their squares. In this way, the areas change dynamically to give a feel of what is happening. The squares of each side are divided into units by a grid.