Obtuse Triangle

Pronunciation: /əbˈtus ˈtraɪˌæŋ gəl/ Explain

An obtuse triangle is a triangle where one of the angles is an obtuse angle. [1][2] An obtuse angle is an angle with a measure of more than 90° (π radians). See figure 1. Since all triangles that do not have a right angle are scalene triangles, all obtuse triangles are obtuse scalene triangles.

obtuse triangle
Figure 1: Obtuse scalene triangle


  1. Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid. pg 8. Translated by Casey, John, LL. www.archive.org. D. F.R.S.. Hodges, Figgis & Co.. 1890. Last Accessed 1/2/2010. http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/8/mode/1up/search/obtuse. Buy the book
  2. obtuse triangle. merriam-webster.com. Encyclopedia Britannica. Merriam-Webster. Last Accessed 12/21/2009. http://www.merriam-webster.com/dictionary/obtuse triangle.

More Information

  • McAdams, David E.. Obtuse Angle. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 3/12/2009. http://www.allmathwords.org/en/o/obtuseangle.html.

Cite this article as:

McAdams, David E. Obtuse Triangle. 5/5/2011. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/o/obtusetriangle.html.

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Revision History

12/21/2009: Added "References". (McAdams, David E.)
8/26/2008: Revised references to 'scalene' and revised 'More Information'. (McAdams, David E.)
7/12/2007: Initial version. (McAdams, David E.)

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