Talk:Menelaus's theorem

Article title
This title was chosen after doing a google count of variations: Update: actually, it seems like Google does not distinguish between "Menelaus' theorem" and "Menelaus theorem", so item 2 above probably includes counts of Menelaus' as well. Now I think "Menelaus' theorem" is a better title since it has consistency with how theorems are generally named.--Tokek 06:44, 8 Feb 2005 (UTC)
 * Theorem of Menelaus: 185 hits
 * Menelaus theorem: 2180 hits
 * Menelaus' theorem: 2180 hits
 * Menelaus's theorem: 552 hits

Update2: it seems like one query can also count other results, e.g. searching for "menelaus theorem" results in also counting "menelaus's theorem" so the google way isn't a very good way of finding out what is the most popular. I will create redirects for now of the four that I think are reasonable titles.

About the equation
According to the Chinese Wikipedia and my math textbook, the right-hand side of the equation should be 1, instead of -1. The common assumption in school(the high school I attend, at least)is that length measurements are restricted to being a positive value, which in turn restricts the value of the right-hand side to 1. The idea that a length value can be negative is a bit confusing. Please correct me if I am mistaken. Thomas Yen 14:18, 11 September 2007 (UTC)


 * Well, you cannot simply change the formula without changing the rest of the text, including the explanation of what negative lengths mean in this context. I changed the article so that it allows both formulations. I hope that the current version agrees with your textbook, in which case I would be grateful if you could add it as a reference. -- Jitse Niesen (talk) 14:40, 14 September 2007 (UTC)

Menelaus's theorem is in fact supposed to have a -1 in it. The reason why is because the orientation of segments matter: AB=-BA. Otherwise the trigonometric version of Menelaus's theorem would yield a different result. Qoou.Anonimu (talk) 01:53, 31 December 2008 (UTC)

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I think that the equation along with the subsequent explanation, as they are now, are just wrong: either you take unsigned segments and assert that the product equals 1, or take signed segments and equal the product to -1.

If no one convinces me on the contrary in the next few days, I will change again the 1 to -1.

Jose Brox (talk) 14:55, 6 November 2013 (UTC)

Dual?
Does someone have a source for the claim that this is dual to Ceva? In my opinion this is an erroneous claim. Tkuvho (talk) 15:58, 6 October 2010 (UTC)

I found corroboration on From Funk to Hilbert geometry Athanase Papadopoulos and Marc Troyanov on page 63

Jackass
What jackass has an absolute value evaluating to minus one?


 * Thank you for pointing that out, it is now corrected. --Bill Cherowitzo (talk) 20:06, 27 November 2019 (UTC)