Double lengths in the regular heptagon
This figure shows all segments in a regular heptagon that are of length 2. The meaning of "all segments" is that their end points are defined as intersections of diagonals (or sides) of the heptagon.
There are 42 segments with this property. Because of rotation and reflection symmetry, only 3 of these are essentially different.
This output was generated by the RegularNGons software tool. You may give it a try in your browser at the URL http://prover-test.geogebra.org/~kovzol/RegularNGons/?n=7&u=2.