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mini equilateral over mega equilateral (Posted on 2021-01-28) Difficulty: 3 of 5
Let n be a natural number. Determine the minimal number of equilateral triangles of side 1 to cover the surface of an equilateral triangle of n + 1/2n

No Solution Yet Submitted by Danish Ahmed Khan    
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Answer | Comment 1 of 2
A simple lower bound is given by the ceiling of the squared area of the larger triangle.

(n+1/(2n))^2 = n^2 + 1 + 1/(4n^2)

The last term is positive and smaller than 1, so the ceiling is n^2+2.

This gives a lot of room to spare and it achievable for any n.  Basically you can start at a corner and tile the first (n-1)^2.  Then put one in each of the other corners.  The remaining equiangular hexagon can be covered by the 2n-1 triangles with minimal overlap.

It's slightly different for even/odd n.  I'll make a picture if I get a chance. 

  Posted by Jer on 2021-01-28 08:30:10
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