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3D. Explanation of Invariance of the sum of squares of distances by using the Steiner theorem.

n/2 points of A1,...,An may be moving on the surface of a sphere of radius r. Each point has antipodal point on a sphere . Thus, the center of gravity is the centre of the sphere.  It is shown, that the sum of squares of distances from any point D of a sphere to →{Ai} , divided by radius squared, is always equal of twice the number of points. https://en.wikipedia.org/wiki/Parallel_axis_theorem https://en.wikipedia.org/wiki/Antipodal_point