Talk:Strophoid

Expert
Before, the article consisted of just, "A curve: r = asin(α − 2θ) / sin(α − θ)". I added the 1911 Encyclopedia Britannica article, but the equations weren't scanned accurately. I looked up the equations on Google, but they didn't even seem close, so I removed the commentary. The article could use an expert to look it over. Perhaps someone can figure out what the 1911 EB was talking about. -- Kjkolb 10:37, 13 November 2005 (UTC)

Mathworld lists it as "r = a cos(2θ) sec(θ)" which is the same upto rotation of cordinates. Having it as asin(...) could cause real confusion with the arcsin function. --Pfafrich 21:01, 31 December 2005 (UTC)

Foot of perpendicular
What is a foot of perpendicular? I couldn't find a definition in Wikipedia.

&mdash;Bartosz 01:51, 27 April 2007 (UTC)
 * updated the drawing --Duk 09:23, 30 November 2007 (UTC)
 * In the process of rephrasing the definition this expression is now gone. For future reference, the foot of a perpendicular (meaning a line perpendicular to a given line) is the point where the lines intersect.--RDBury (talk) 17:25, 21 July 2009 (UTC)
 * Added this to Wiktionary.--RDBury (talk) 17:25, 21 July 2009 (UTC)

Variations in terminology
The term strophoid has several meanings depending on the source. Yates, Lockwood and MathWorld (see refs. in article) give a very generalized meaning of the term and use the phrase "right strophoid" for the specific special case used by some, e.g. Springer Enc. of Mathematics and 1911 Encyclopedia Britanica. Yates and Lockwood also use the term "oblique strophoid" to describe a slight generalization of the right strophoid. I think Yates and Lockwood are the more authoritative sources and it's better to have the more general term used in the article (rather than having to invent names like "generalized strophoid") so I'm going to try to change the terminology in the article from what is being used now (basically taken from 1911 EB) to that of Yates and Lockwood. People trying to find "strophoid" in the 1911 EB sense will still find the material in the same article, though perhaps a bit further down, so I don't think the change will confuse people.--RDBury (talk) 04:33, 20 July 2009 (UTC)
 * Note, corrections made to the preceding paragraph.--RDBury (talk) 18:21, 21 July 2009 (UTC)

AP1 and AP2 are perpendicular?
The first paragraph contains this sentence: "Note that AP1 and AP2 are at right angles in this construction." How can this be true? if the line L intersects A, then AP1 and AP2 will be at 180 degrees from each other, not at a right angle. -- Wingedsubmariner (talk) 05:24, 28 August 2015 (UTC)

Wiktionary definition needs improvement
As I'm not a geometer, I'm not sure how best to condense the rather technical definition here into a decent one-liner. Equinox ◑ 22:23, 29 January 2018 (UTC)