“3D Thinking” Page 131: An animation of the Pythagorean Theorem shown dynamically in terms of circles or spheres. In the animation the diameter of the outer circle/sphere equals the hypotenuse of the right-angled triangle. The diameters of the two inner circles/spheres equal the lengths of the other two sides of the right-angled triangle. According to the Theorem of Pythagoras the sum of the surface areas of the two inner circles/spheres always equals the surface area of the outer circle/sphere. The animation rotates the right-angled corner of the triangle around the circumference of the outer circle/sphere. Pythagoras’ theorem states that the square of the hypotenuse (area) equals the sum of the squares (areas) of the other two sides….There’s a balance to the animation – a sort of harmony of proportion.