Given a regular hexagon with center on the origin of an x-y plane
with coordinate (r,0) on the x axis, we are to express the
coordinates of "A" located at 120 deg from (r,0) in terms of "r".
It is easiest to find the coordinates of A if you think of the hexagon as 6 equilateral triangles. Each side of these triangles are of length r. Since the y axis creates a 30-60-90 triangle where A is one of the vertices, it is pretty easy to find the remaining sides of the triangle. The length of these sides will help you find the coordinate point for A.
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