How to make a regular pentagon from technic bricks For the purposes of this build, we need a pentagon (figure with 5 sides), that is regular (all sides have equal length), and it needs to be able to be mounted on a build (like a wreath) by a technic-friction-pin, (the little black ones).

This may be hard to achieve, with the given possible angles. The pentagonal shape must maintain its shape, no warping, etc. It must also be made of "properly fitting pieces."
Using the same length ratios as in the construction that Philo posted in his answer I created this:




It uses length 5, 6 and 7 thin liftarms (5 of each) and 30 half-pins
I'm quite happy with it!