Talk:Quadrilateral

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[edit] How has this page helped you?

This page helped me in my studies for a math test.--Pure-intellect (talk) 19:13, 8 January 2008 (UTC)

[edit] Trapezoid/trapezium

I could have sworn that the two sides parallel ones are called "trapezoids". --BlackGriffen

And you would have been right. I've made the change. Vicki Rosenzweig

The article thus far lists only cyclic quadrilaterals; can someone who's done geometry within the last 20 years fix this? Vicki Rosenzweig (yes, me again)

The trapezoid is three dimensional.

--- User:Karl Palmen

I've always known a trapezoid to be two dimensional, and Trapezium to be a trapezoidal object associated with astronomy. -- Olof
Wolfram's MathWorld [1] gives: "There are two common definitions of the trapezium. The American definition is a quadrilateral with no parallel sides. The British definition for a trapezium is a quadrilateral with two sides parallel." and "The trapezoid is equivalent to the British definition of trapezium." -- Olof

Could a British speaker confirm this? Also, is "trapezoid" used in Britain, and if so, in what meaning? Maybe this should be added to American and British English Differences. AxelBoldt

I'm not sure about "trapezoid", but a trapezium definitely has two parallel sides in British usage. --Zundark, 2002 Mar 11
I second Zundark. BTW, to whoever did the picture: it's excellent! -- Tarquin 13:38 Aug 20, 2002 (PDT)
American and British English Differences is a page of general differences. This specific difference belongs and already is on List of words having different meanings in British and American English. -- Smjg 15:14, 26 Jul 2004 (UTC)

[edit] Taxonomy is wrong, or is it?

A parallelogram is a special case of a trapezium, not an isosceles trapezium. An isosceles trapezium has adjacent angles equal and opposite angles generally unequal; a parallelogram has opposite angles equal and adjacent sides generally unequal.

In precisely the same way, a rhombus is not a special case of a 3-sides-equal trapezium, only of kite and parallelogram.

But a square is a special case of a 3-sides-equal trapezium.

-- Smjg 15:14, 26 Jul 2004 (UTC)

Meanwhile, I've put back the ASCII taxonomy graph and expanded on it a bit. If anyone would like to do this one up as an image, I'll leave it up to you.... -- Smjg 14:05, 27 Sep 2004 (UTC)

Diagram now fixed. Gdr 19:51, 2004 Oct 19 (UTC)

[edit] Picture

The picture at the bottom of this article is wrong. It says that a parallelogram is always an isosceles trapezoid. A non-rectangular parallelogram as rotational symmetry; an isosceles trapezoid has reflection symmetry. These mismatch so these are 2 separate kinds of quadrilaterals where the rectangle is the special case of both. Any comments on this?? 66.245.28.124 22:27, 19 Oct 2004 (UTC)

See above. The diagram is fixed but the old version is still in Wikipedia's image cache. Gdr 22:40, 2004 Oct 19 (UTC)

also....stuff like this are really boring.....really really boring.



HAPPY CHRISTMAS TO ALL RAMADANS!

[edit] Square in the diagram

The square in the diagram doesn't look like a perfect square as I can see by rotating it. Georgia guy 16:45, 15 May 2005 (UTC)

Which diagram? Gdr June 28, 2005 08:28 (UTC)

[edit] The classification picture

There could be tangential quadrilaterals which are also trapezoids. No? --203.186.238.243 9 July 2005 16:02 (UTC)

Indeed. Even tangential quadrilaterals which are also right-angled trapezia. (But not every tangential quadrilateral is a trapezium.) You're welcome to extend the diagram to add the new categories, though I think "cyclic right-angled trapezium" might be a bit obscure... Gdr 12:55:55, 2005-08-03 (UTC)

[edit] arrowhead/chevron

Arrowhead: the forgotten quadrilateral. From memory this is the shape that adorned the uniforms of the crew of the USS Enterprise in the original Star Trek - though perhaps a more formal definition is called for. I open the bidding with "a quadrilateral with an internal reflex angle". Why is the arrowhead grievously overlooked (it's not in Encarta for instance)? Is the correct term Arrowhead or Chevron or is this the nameless as well as the forgotten quadrilateral? On the face of it this shape deserves a separate mention alongside rectangle, rhombus etc. —The preceding unsigned comment was added by Brainfood (talk • contribs) .

The reflex angle is covered by "concave quadrilateral". I assume you mean a sort of concave kite with pairs of equal sides. --Henrygb 12:20, 24 January 2006 (UTC)

[edit] Quadrilatère complet

hello, I am french and my english is not very good. I have just a question: how do you call this figure (in french fr:quadrilatère complet). Thank you. HB

We call it a complete quadrilateral in English too.--Syd Henderson 03:20, 19 August 2006 (UTC)

[edit] Template

Any opinions on a template for quadrilaterals?? Georgia guy 16:33, 21 June 2006 (UTC)

[edit] added "not" a square, to definition of oblong (rectangle)

I went ahead and made this change in "The square as a rectangle" section of article., as I am pretty sure it was a simple mistake (i.e., "A rectangle that is not a square is an oblong." was the intended statement). I think more qualification might be necessary, as the term 'oblong' is only relevant if a square is included in the definition of rectangle (which I think among mathematicians it always is), but I sink pretty fast in these terminological quagmires, especially if I am making any attempt to cultivate one. Jauntymcd 11:44, 20 March 2007 (UTC)

[edit] Complex quadrilateral

In Coxeter's book Regular complex polytopes, a complex quadrilateral is a quadrilateral in the unitary plane, which is quite a different beast - it involves complex numbers and is kind of four-dimensional (two real dimensions and two imaginary ones). So where does the use of "complex" meaning self-intersecting (not simple) come from? Can somebody give a reference? -- Steelpillow 22:30, 5 July 2007 (UTC)

I'm sure it is talking about this meaning: Complex polygon#Computer graphics. Tom Ruen 22:45, 5 July 2007 (UTC)
Yes I am sure it is. And that page doesn't have an explanation or a reference for it either. In fact, I added the heading on 23 December 2006, in order to distance the content from the way Coxeter used the term. I don't actually know whether the "non-convex" usage is confined to computer graphics. I noticed that its use in this context was widespread on t'Internet, and again I don't know whether this is because it always has been or whether this presence has grown entirely due to people copying from Wikipedia. I had hoped that someone with better knowledge would either correct or confirm my heading (and add a reference!), but in six months - nothing. -- Steelpillow 22:03, 8 July 2007 (UTC)

[edit] Contradictory statements

The article says both

  • Trapezium (in British) or trapezoid (American English): no sides are parallel.
  • Trapezium (British English) or trapezoid (Amer.): two opposite sides are parallel.

I have no idea which of the two is correct, so I'm not changing anything, but clearly one of the two has the Brit and American names swapped.99.130.29.223 07:46, 10 November 2007 (UTC)

[edit] UK / US usage

I was always taught at school (in the UK in the seventies and eighties) that a trapezium has one pair of parallel sides and a trapezoid has none. Is this a difference is UK / US usage, i.e. that a UK trapezium is the same as a US trapezoid and vice versa? The UK meaning of trapezoid is missing from the article, and Wiktionary lists it as "obsolete". Can anyone clarify this? HairyDan (talk) 12:18, 23 March 2008 (UTC)

[edit] Brahmagupta's formula

Shouldn't there be mention of Brahmagupta's formula?  Laptopdude  Talk  21:36, 25 April 2008 (UTC)