
Re: BUSTED! Re: Mythbusting pentagons by compass & straight edge.
Posted:
Aug 21, 2013 12:20 PM


I'll offer the same wellsupported advice to you; please stop embarrassing yourself. You, along with Jonathan I assume, are using a modern wellmachined compass that actually locks. Mine was always the cheapee backtoschool variety that modifies its radius along the way. But mine was far better than the collapsible compass of the ancient Greeks maybe drawn the sand. Your well machined compass that locks precisely on a radius but then collapses works very well for the regular 3gon and 6gon and it's a little tricky for a 4gon but try it for a 12gon and then we'll talk. Much easier, in a sense, is draw yourself a line segment, locate a point on another line somewhere, and copy the line segment on the line at the point (either direction, I don't care) using your very precise, wellmachined collapsible compass.
Wayne
At 01:47 AM 8/21/2013, GS Chandy wrote: >[Message resent] >+++++ >Wayne Bishop (WB) posted Aug 19, 2013 9:35 AM: > > > > The "myth" has always been in your brain not in the > > mathematics. In > > 6th grade it was obvious to me that constructing a > > regular hexagon > > with a compass was a triviality (and understood the > > trivial > > underlying mathematics) but had already observed > > that, if I really > > wanted a regular hexagon, not a cute construction > > were the final arc > > never hits the starting point, I should use a > > protractor. It's the > > proof that matters and, even more so, that the > > regular septagon can > > NOT be so constructed, not some Easter Bunny in your > > head. Why > > persist in embarrassing yourself? > > > > Wayne > > >I observe that the construction of a regular hexagon with compasses >and straightedge (to draw the sides) was never a problem at all (in >the 6th grade or even earlier, as I recall). The final arc, more >often than not, did hit the starting point or got so very close that >the error didn't matter at all. I tried it some time ago, and it >worked just fine. Whether during our schooldays, or now, a >protractor is needed only to reconfirm the angles  the 'protractor >construction' is in any case only approximate  it will NEVER be >100% accurate. Your example (or lesson, if that was what you were >planning to help us draw from it) fails. > >Jonathan Crabtree (JC) has been facing some some problems with the >pentagon, as have I. I suspect the reason is that we're both making >some minor errors at various steps, which add up cumulatively in the >rather more complex steps of the construction. These minor errors >add up and one gets a fifth side that is quite significantly >different in many cases. By the way, my architect friend came back >to me with a pretty welldrawn (and adequately accurate) pentagon  >he did confess that he'd had some trouble getting there. (And yes, >I can confirm that one does get a sense of 'going crazy' when one >sees errors in something that one KNOWS should fetch you a right result). > >I found a couple of interesting links to 'approximate pentagon >construction': one is the regular story at Wikipedia: >http://en.wikipedia.org/wiki/Heptagon > >The other is http://hptgn.tripod.com/heptagon.htm. > >I read through both of the writeups, but did not try to do any of >the constructions. > >I really don't see where JC has been "embarrassing himself" as you >claim he has been. The Easter Bunny and the septagon (heptagon??) >are a different matter, of course. > >By the way, I might observe that mathematicians as eminent as John >Horton Conway (not to mention Euclid, of course) apparently spent >considerable time and effort with these 'compassandstraightedge >constructions' without feeling embarrassed about the matter AT >ALL! So I don't understand why JC (or I, for that matter) should >feel "embarrassed" about sharing our thoughts on difficulties faced >in 'getting a pentagon right'. > >In my view, things that really should embarrass are weird slogans like: > >  "BLOW UP THE SCHOOLS OF EDUCATION!" (whether it belongs to Reid >Lyon or to you; whether meant literally or metaphorically or delusionally); > >  "PUT THE EDUCATION MAFIA IN JAIL!"; > >  "Children must be PUSHED to learn math (or anything >else). ENCOURAGEMENT not the issue". > >IMHO, these should REALLY be embarrassing! > >Why persist in embarrassing yourselves?? !!! > >GSC >("Still Shoveling! Not PUSHING!") > > > At 04:16 PM 8/18/2013, Jonathan Crabtree wrote > > >"Although they make use of the visible forms and > > reason about them, > > >they are not thinking of these, but of the ideals > > which they > > >resemble, not the figures which they draw..." > > > > > >So in conclusion, the myth is busted and my > > relationship with Euclid > > >is now merely Platonic. > > > > > >Jonathan Crabtree > > >Mathematics Researcher > > >Melbourne Australia > > >(Currently over at http://bit.ly/Vrrx9Q)

