n/2 points of [color=#0000ff]A[sub]1[/sub],...,A[sub]n[/sub][/color] may be moving in a circle of radius r. Each [color=#0000ff]point[/color] has [color=#ff7700]antipodal point[/color] on the circle. Thus, the center of gravity [color=#ff00ff]Cm[/color] is the centre of the circle. [br] It is shown, that the sum of squares of distances from any point [color=#ff0000]D[/color] of a circle to → {[color=#0000ff]A[sub]i[/sub][/color] } , divided by radius squared, is always equal of twice the number of points. [br][url=https://en.wikipedia.org/wiki/Parallel_axis_theorem]https://en.wikipedia.org/wiki/Parallel_axis_theorem[/url][br][url=https://en.wikipedia.org/wiki/Antipodal_point]https://en.wikipedia.org/wiki/Antipodal_point[/url]