# Obtuse Triangle

Pronunciation: /əbˈtus ˈtraɪˌæŋ.gəl/ Explain

 Figure 1: Obtuse triangle

An obtuse triangle is a triangle where one of the angles is an obtuse angle.[1] 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 also obtuse scalene triangles.

 Click on the blue point and drag it to change the figure. This manipulative will only show obtuse triangles. What definition can you give for obtuse triangles? Manipulative 1 - Obtuse Triangle Created with GeoGebra.

### References

1. McAdams, David E.. All Math Words Dictionary, obtuse triangle. 2nd Classroom edition 20150108-4799968. pg 129. Life is a Story Problem LLC. January 8, 2015. Buy the book
2. 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 9/5/2018. http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/8/mode/1up/search/obtuse. Buy the book

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

McAdams, David E. Obtuse Triangle. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/o/obtusetriangle.html.

### Revision History

12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)