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MathNet 2019-part-02 — 184 problems (EN–VI) Question 156

Math Olympiad Vault · MathNet 2019-part-02 — 184 problems (EN–VI)

Question 156

Let $\mathcal{C}$ be a circle of radius $1$, and let $T$ be a real number. We say that a set of triangles is $T$-merarious if it satisfies the following three conditions:

$\triangleright$ the vertices of each triangle belong to $\mathcal{C}$;
$\triangleright$ the triangles have pairwise disjoint interiors (but two triangles may share a side or a vertex);
$\triangleright$ each triangle has perimeter strictly greater than $\mathbf{T}$.

Find all real numbers $\mathbf{T}$ such that, for every integer $\mathrm{n} \geqslant 1$, there exists a $T$-merarious set containing exactly $n$ triangles.