is an equilateral triangle of side 2010. Also is a square. What is the radius of the circle?
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Let F be a point in BCDE such that DEF is an equilateral triangle. Then, observe that AFEB is a parallelogram since AB is equal and parallel to EF, thus A F = B E = E D = F E = F D , so F is equidistant from points A , E , D . Hence, F is the center of the circle, which means that the radius is 2010.
Note: The above solution relies on "make this wonderful observation", which I typically do not like.
The proper way to find the circumcenter of A E D would be to take the perpendicular bisectors. However, it is not immediately obvious how/where the perpendicular bisectors of A E and A D would intersect. Hence, I present the above solution, instead of a tedious coordinate geometry solution.