Let be distinct interior points of a regular hexagon with side length . Assume that no three points of the set
are collinear. Show that there is a triangle with area less than all of whose vertices belong to .
Solution
Draw line segments from to the points , we get six smaller triangles. Since any three points in are not collinear, is inside one of the six triangles. Draw line segments joining with the vertices of this triangle to divide it into three triangles. The total number of triangles is increased by . Do the same for the points to subdivide the hexagon into non-overlapping triangles, each time the total number of triangles is increased by . Thus, after the construction, the total number of triangles is . If the area of each of these triangles is , then the area of the hexagon is , which is a contradiction.
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