How do I find the moment of inertia of a regular N-gon?

Answer 1

Assuming you mean about a perpendicular axis through the center of the n-gon, with uniform mass density, I would point out that the n-gon can be divided into n isosceles triangles with vertices at the rotation axis. The total moi would then be just n times the moi of an isosceles triangle rotated about its apex.