A unit square and a circle have the following property: if is a point in the plane not contained in the interior of , then . The minimum possible area of can be expressed as for relatively prime positive integers and . Compute .
Solution
Note that the condition for in the problem is equivalent to the following condition: if , then is contained in the interior of . Let , and be the four points in such that , and are all equilateral triangles. Now, let , and be the respective circumcircles of these triangles, and let the centers of these circles be , and . Note that the set of points such that is the intersection of , and . We want to find the area of the minimum circle containing this intersection. Let and intersect at and . Define and similarly. It is not hard to see that the circumcircle of square is the desired circle. Now observe that . Similarly, , so is equilateral. Its height is the distance from to , which is , so its side length is . This is also the diameter of the desired circle, so its area is .