# Rigid regular nonagon from 21 Meccano strips

You are given 21 Meccano strips, where the distance between adjacent holes is 1 unit:

• 9 strips of length 10 (hence having 11 holes)
• 6 strips of length 18 (19 holes)
• 6 strips of length 19 (20 holes)

By inserting nuts and bolts in the holes so as to form hinges between the strips, it is possible to create a rigid framework where

• portions of nine different strips form a perfectly regular nonagon of side length 6 (with vertices coincident with hole centres)
• no strip is redundantly long, i.e. all end holes are part of some hinge linking at least two different strips

Can you find this rigid framework and prove its rigidity?

• Do you already know the answer, and are posing it as a puzzle, or do you not know the answer, and are asking out of curiosity? Commented Dec 3, 2021 at 14:38
• @user21820 I know the answer and it is somewhere on MSE. Commented Dec 3, 2021 at 15:14
• My first guess is no simply because it's not constructible, but if you say it's "yes" then I've no idea. Commented Dec 3, 2021 at 15:25
• @user21820 for what it's worth, I have found the solution on MSE, and it is not what I expected - if anyone is still interested in this puzzle, your first instinct to use the 9 identical pieces as the sides and the others as scaffolding is terribly wrong :-) Commented Apr 29, 2022 at 12:11
• @htmlcoderexe: Yes I saw that post already last year because I went to look for it. Thanks for telling me though! =) Commented Apr 29, 2022 at 12:16