CWMO 2012 Problem 2

Show that among any $n\geq 3$ vertices of a regular $(2n-1)$ -gon we can find $3$ of them forming an isosceles triangle.

Dataset text AI-MO AoPS. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.