Let be a triangle with , and . Let be points on side , be points on side , and be points on side . Suppose that there exists a point such that , and are congruent equilateral triangles. Find the area of convex hexagon .
Solution
Since is the shared vertex between the three equilateral triangles, we note that is the incenter of since it is equidistant to all three sides. Since the area is 6 and the semiperimeter is also 6, we can calculate the inradius, i.e. the altitude, as 1, which in turn implies that the side length of the equilateral triangle is . Furthermore, since the incenter is the intersection of angle bisectors, it is easy to see that , and . Using the fact that the altitudes from to and form a square with the sides, we use the side lengths of the equilateral triangle to compute that , and . We have that the area of the hexagon is therefore
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