Talk:isosceles triangle

I am horrified to see that both Wikipedia and Wiktionary have incorrect (by original definition) formal definitions of the word isosceles. Is this an example of "divided by a common language", or just loose thinking? I intend to put the formal Euclidean definition first, but retain the modern (mis-used) definition because some websites and texts use this. Which definition do American schools use? USA websites seem to give contradictory answers.  D b f  i  r  s   22:40, 16 January 2008 (UTC) The error (IMHO) seems to have originated with Eric W. Weisstein. Was he thinking of the classification of quadrilaterals, where there are many subsets? Triangles have always been classified into three disjoint sets: Scalene, Isosceles OR Equilateral.  D b f  i  r  s   22:59, 16 January 2008 (UTC)

According to MathWorld] - "An isosceles triangle is a triangle with (at least) two equal sides." SemperBlotto 23:06, 16 January 2008 (UTC)
 * That was the point I was making. Eric W. Weisstein in Mathworld seems to have collected an erroneous definition, and confusion seems to have spread from there.  I can provide three citations from early Euclidean geometry which define an "isosceles triangle" to be one which has EXACTLY two equal sides.  Why did the Wiki community opt for Eric W. Weisstein's view?  Is this definition the usual one in the USA?  I haven't changed anything yet, because I would like to find out usage outside England.    D b f  i  r  s   23:30, 16 January 2008 (UTC)
 * Now changed, trying to provide NPoV. I even put the Eric W. Weisstein interpretation first!  My research suggests that schools and students are very confused over this definition.  What does anyone else think?   D b f  i  r  s   13:01, 17 January 2008 (UTC)
 * (after contacting MathWorld) To be fair to this excellent website, they did put forward an excellent rationale for adopting the inclusive definition (to make Euclid's proof of isosceles triangle more watertight, and for consistency with inclusive definitions of special quadrilaterals), so the "wrong" (IMHO) definition can remain first, even though Euclid himself categorised triangles into three disjoint types.   D b f  i  r  s   18:38, 19 January 2008 (UTC)


 * All squares are rectangles but not all rectangles are squares, said Euler.

I undid my edit.
Just to make sure you know, I made an edit an then undid it so that it would go with the "Usage notes" section. So now that my undo was undone, it now says "at least" again, like it did in my original edit, as if there weren't any "undoes" in the first place. Just letting you know. The Sackinator (talk) 15:52, 16 May 2015 (UTC)
 * Oh, I actually was notified that my first edit was correct, so, maybe I was okay after all. The Sackinator (talk) 15:53, 16 May 2015 (UTC)

RFD discussion: February–September 2019

 * See Talk:acute-angled triangle.