Theorem The smallest regular hexagon cover for the family of all triangles of
perimeter two is the regular hexagon of diameter one (the area is
8
3 3 ).
Proof. Let R be the regular hexagon of diameter one and let T be a triangle of
perimeter two. We label the vertices of the triangle T by A, B and C where the
angle ∠A is greater than or equal to the angle ∠B, and the angle ∠B is greater
than or equal to the angle ∠C. We divide the triangle T into two cases.
Case 1. The diameter of the triangle T is at most 5
6
.
Let P and Q be two points on the perimeter of the regular hexagon R such that
the distance between P and Q is equal to 5
6
and the segment PQ is parallel to a
diagonal of the regular hexagon R as shown in Fig. 1. We see that the distance
between the vertex D and the segment PQ is equal to 1
3
. Moreover, we note
that the thickness of the regular hexagon R is greater than 5
6
as shown in Fig. 1.