The diagram is intentionally misleading. So, instead, note that 18*10=180. Array ten of these triangles around their common 18 degree corners. This inscribes in a semicircle of radius 2 whose length is 2*PI. so 10x<2*p or x<0.62832...

Of course this is not the precise answer you have challenge us to find, but it's better than nothng!

[Disclaimer: I am not a member so I could only read the first few paragraphs of this piece. Apologies in advance if I am discussing something already covered by it. AT]