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Solution to the Regular Hexagons Problem

This was not a challenge in the Naturally Mathematical Challenges, but just came as an idea as a result of the hexagon-based challenge.

To find the solution, it really helps to look at simpler cases first. If you do that, you will soon find that a remarkable pattern emerges. Here, we'll summarise the number of hexagons of each side-length that can be found in a larger figure. As we count the number of hexagons in a hexagon of side n, we find that there is 1 of side n, 2 + 3 + 2 = 7 of side n - 1, and so on.

Largest ________ Smallest
... n
3 ... n+1
2 4 ... ...
1 3 5 ... 2n-1
2 4 ... ...
3 ... n+1
... n

After examining the cases for n = 1, 2 and 3, it seems reasonable to make the hypothesis that  Hn= n3, i.e. that the number of regular hexagons in a hexagon of side n is n3. H1=1 is true. If Hn= n3 is assumed true, then

This reduces to Hn+1=(n+1)3.

Hence by mathematical induction, Hn= n3 is true for all n.

For an alternative, and very insightful solution, have a look at David King's method of proof!