# Talk:Triangle

Triangle is a former featured article. Please see the links under Article milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.
This article appeared on Wikipedia's Main Page as Today's featured article on May 14, 2004.
Article milestones
DateProcessResult
May 5, 2004Featured article candidatePromoted
February 25, 2005Featured article reviewDemoted
January 4, 2006Good article nomineeListed
January 17, 2006Good article reassessmentDelisted
Current status: Former featured article

WikiProject Mathematics (Rated B-class, Top-importance)
This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of Mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Mathematics rating:
 B Class
 Top Importance
Field:  Geometry
A vital article.
One of the 500 most frequently viewed mathematics articles.
Wikipedia Version 1.0 Editorial Team / Vital (Rated C-class)
C  This article has been rated as C-Class on the quality scale.

## TRIANGLE : 5.3 Solution of triangles

About solution of triangles, 5.3 the next sentence could be more accurate if the last section is added:

"Solution of triangles" is the main trigonometric problem: to find missing characteristics of a triangle (three angles, the lengths of the three sides etc.) when at least three of these characteristics are given , including at least one non-angular value.

Could somebody make this appropriate correction ?

--Duckkcud (talk) 19:51, 7 April 2018 (UTC)Duckkcud 2018-04-07

While appropriate for planar triangles, it is not appropriate for spherical triangles since AAA is a congruency condition there.--Bill Cherowitzo (talk) 03:17, 8 April 2018 (UTC)

For solution of non-Euclidian triangle, you will need more than AAA; you need R ( a non angular value ) to find the length of the sides... In the end exemple of non-planar geometry, the position of the corners give the ratio of surface, but still not the length of the sides... Duckkcud 2018-04-10 — Preceding unsigned comment added by Duckkcud (talkcontribs) 17:05, 10 April 2018 (UTC)

The section specifically includes triangles on a sphere, so any statement made should also be applicable to that case. Also, in the spherical case, the lengths of the sides of the triangle are not measured in linear units (to do so you would need to know R the radius of the sphere, as you correctly point out) but rather in angular units referring to the central angles determined by the sides and this does not require knowledge of R. This, probably, is due to the astronomical applications, where R can not be accurately determined. See the main article Solving Triangles for more information on this. The example in the non-planar triangle section of this article is not germane to this question.

As this article on "Triangles" deals primarely on plane one, it should be normal to precise its properties without confusion. That is exactly precised in the article on "solution of triangle" in wiki: '...at least one of the side lengths must be specified...'

``` https://en.wikipedia.org/wiki/Solution_of_triangles#Solving_plane_triangles
```

The surface, the perimeter can too serve to solution. But only angles, are not enough.

```  http://www.rlefebvre.ca/triangulateur/triangulator.htm
```

In the paragraph that I propose to correct, there is no reference to spherical triangle. So, it is an error to not mention what I propose. DUckkcud 2018 04 11 — Preceding unsigned comment added by Duckkcud (talkcontribs) 13:51, 11 April 2018 (UTC)

The section, in its entirety is:

"Solution of triangles" is the main trigonometric problem: to find missing characteristics of a triangle (three angles, the lengths of the three sides etc.) when at least three of these characteristics are given. The triangle can be located on a plane or on a sphere. This problem often occurs in various trigonometric applications, such as geodesy, astronomy, construction, navigation etc.

What part of "The triangle can be located on a plane or on a sphere." do you not understand? Your statement is valid for planar triangles, and I have said so above, so I am not sure what you intend by bringing up sources which only refer to planar triangles.--Bill Cherowitzo (talk) 18:25, 11 April 2018 (UTC)

I should have written "in the sentence", not "in the paragraph". And calling an error was not appropriate. Excuse me. My intent is to take the occasion to say exactly how many and what inputs are necessary to solution a planar triangle

```without confusion with spherical one.
```

"At least three" is a bit vague while the number 3 is the beauty of triangle. I still suggest: "when three of these characteristics are given , including at least one non-angular value on a plane." --Duckkcud 2018 04 11 — Preceding unsigned comment added by 208.114.128.61 (talk) 21:24, 11 April 2018 (UTC)

## Semi-protected edit request on 22 August 2019

in the "See also" section add "STL (file format)". wikipedia.org/wiki/STL_(file_format) Austinthemighty (talk) 06:22, 22 August 2019 (UTC)

Not done: triangulation is already mentioned as a more general case so specific file format does not seem necessary. Melmann 10:03, 22 August 2019 (UTC)

## Adding the area of a cevian triangle

Hi guys,

Read the "Be Bold" statement so will add a short entry under "Figures inscribed in a triangle" for cevian triangles then pursue a separate entry for this subject.

Dominic — Preceding unsigned comment added by 108.167.57.225 (talk) 12:01, 3 November 2019 (UTC)

Just remember to follow what published reliable sources have said, we don't publish original research or original mathematical proofs and we can't cite forums. – Thjarkur (talk) 12:11, 3 November 2019 (UTC)