Icosikaitrigon construction at 1.2E-11

It is the best solution for Icosikaitrigon construction.It take tow days to simplify the methid which can be finished in normal compass and straight method.

Enneadecagon construction at 1.6E-11

this is the solution for compass and straight to construct a Enneadecagon with least error at 1.6E-11.

tridecagon construction at error 7.6E-11

It is not a good method but the error is the best one so far. I post here for memory.

construction a perfect Enneadecagon-1

Enneadecagon (regular polygon with 19 sides) is also not constructable in theory. But there is some classic construction method with error 0.02 ° for the angel. Consider the accumulation error,the total erroe will be 19x0.02=0.38° which can be found by regular compass.

I had tried times and found a way to construct Enneadecagon with very little error. See right picture for details.

The idea is to construct a angel of 6 time Enneadecagon angel(360/9). Since 19 is a primer, so it is easy to use this angel to construct a perfect Enneadecagon if we can have a perfect 6 times angel.

The angel I found has error of 1E-5, the constructed Enneadecagon angel has error of 2E-5,so even for a big compass, you will be not able to find out the error as the max error is 0.00017° after construction the whole Enneadecagon。

If you not familiar for the construction with this 6time angel, see next section for details.