Iterated Pedal Triangles

Problem

Triangle A0B0C0A_0B_0C_0 has interior angles 59.999∘59.999^\circ, 60∘60^\circ, 60.001∘60.001^\circ. For each positive integer nn, let AnA_n be the foot of the perpendicular from An−1A_{n-1} to side Bn−1Cn−1B_{n-1}C_{n-1}, and define BnB_n and CnC_n analogously. Find the least positive integer nn for which triangle AnBnCnA_nB_nC_n is obtuse.

Answer

Solution

Difficulty7/10
Topicsplane geometry, trigonometry, Recursion, sequences, Triangle Geometry

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