Information About

Heptadecagon




In Geometry , a heptadecagon (or '''17-gon''') is a seventeen-sided Polygon .
A regular heptadecagon has Internal Angle s each measuring rac{2700}{17} = 158 rac{14}{17} \approx 158.82 degrees.


HEPTADECAGON CONSTRUCTION

The regular heptadecagon is a Constructible Polygon , as was shown by Carl Friedrich Gauss in 1796. Gauss was so pleased by this that he asked for one to be inscribed on his Tombstone . The stonemason declined, stating that the difficult construction would essentially look like a circle.

Constructibility implies that Trigonometric Function s of 2π/17 can be expressed with basic Arithmetic and Square Root s alone. Gauss' book ''Disquisitiones'' contains the following equation, given here in modern notation:

:16\,\operatorname{cos}{2\pi\over17}=-1+\sqrt{17}+\sqrt{34-2\sqrt{17}}+2\sqrt{17+3\sqrt{17}-\sqrt{34-2\sqrt{17}}-2\sqrt{34+2\sqrt{17}}}.

The first actual method of construction was devised by Johannes Erchinger, a few years after Gauss' work, as shown step-by-step in the animation below. It takes 64 steps.


SEE ALSO



EXTERNAL LINKS


You can see how to construct a regular 17-gon geometrically at either of

:http://www.showmath.co.kr/const/polygon/rpoly17.html (Korean, flash)
:http://www.geocities.com/RainForest/Vines/2977/gauss/formulae/heptadecagon.html
:http://mathworld.wolfram.com/Heptadecagon.html
:http://www.jimloy.com/geometry/17-gon.htm

And you can see the Algebra ic aspect (by Gauss) in this book:

'Famous Problems and Other Monographs' by F.Klein et al.

:http://www.mathlove.org/bbs/data/mathfb/alg17gon.ppt