Right Angle
Pronunciation: /raɪt ˈæŋ.gəl/ Explain
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Can you find all 5 angle classes represented?
 Manipulative 1  Angle Classes Created with GeoGebra. 

Angles
are divided into four classes according to their measure. A
right angle is an angle that measures
1/4 of a full circle^{[2]}.
Classes of Angles
Degree Measure  Radian Measure  Class Name 
α < 90° 
α < π / 2 rad. 
Acute angle 
α = 90° 
α = π / 2 rad. 
Right angle 
90° < α < 180° 
π / 2 < α < π
rad. 
Obtuse angle 
α = 180° 
α = π rad. 
Straight angle 
180 < α < 360° 
π < α < 2π
rad. 
Reflex angle 
α = 360° 
α = 2π rad. 
Full angle 
Table 1: Classes of angles 

References
 McAdams, David E.. All Math Words Dictionary, right angle. 2nd Classroom edition 201501084799968. pg 157. Life is a Story Problem LLC. January 8, 2015. Buy the book
 Keller, Samuel Smith. Mathematics for Engineering Students, Plane and Solid Geometry. pg 2. www.archive.org. D. Van Nostrand Company. 1908. Last Accessed 12/4/2018. http://www.archive.org/stream/mathengineer00kellrich#page/2/mode/1up/search/right. Buy the book
 Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid. pg 7. Translated by Casey, John, LL.D. F.R.S.. www.archive.org. Hodges, Figgis & Co.. 1890. Last Accessed 12/4/2018. http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/7/mode/1up/search/right. Buy the book
 right angle. merriamwebster.com. Encyclopedia Britannica. MerriamWebster. Last Accessed 12/4/2018. http://www.merriamwebster.com/dictionary/right angle. Buy the book
Educator Resources
Cite this article as:
McAdams, David E. Right Angle. 5/3/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/r/rightangle.html.
Image Credits
Revision History
5/3/2019: Changed equations and expressions to new format. (
McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (
McAdams, David E.)
12/5/2018: Removed broken links, updated license, implemented new markup, implemented new Geogebra app. (
McAdams, David E.)
8/7/2018: Changed vocabulary links to WORDLINK format. (
McAdams, David E.)
1/1/2010: Added "References". (
McAdams, David E.)
12/14/2009: Added reference to Euclid's Elements. Expanded table of angle classes. (
McAdams, David E.)
9/16/2008: Initial version. (
McAdams, David E.)