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If you have decided that the result holds for a regular hexagon, what is it exactly about the hexagon that lets it work?
What does a regular hexagon also have that isn't needed for this result?
For the regular pentagon, put a point somewhere inside, perhaps not at the centre.
Join that point to each of the vertices of the pentagon and think about the five triangles.
Finally, what does a regular pentagon also have that isn't needed for this result?
Pentagonal
Age 14 to 16
Challenge Level 
If you have decided that the result holds for a regular hexagon, what is it exactly about the hexagon that lets it work?
What does a regular hexagon also have that isn't needed for this result?
For the regular pentagon, put a point somewhere inside, perhaps not at the centre.
Join that point to each of the vertices of the pentagon and think about the five triangles.
Finally, what does a regular pentagon also have that isn't needed for this result?
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