Right Angle

Pronunciation: /raɪt ˈæŋ.gəl/ Explain

Click on the blue point and drag it to change the figure.

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[1].

Classes of Angles
Degree MeasureRadian MeasureClass 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


  1. 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
  2. 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
  3. right angle. merriam-webster.com. Encyclopedia Britannica. Merriam-Webster. Last Accessed 12/4/2018. http://www.merriam-webster.com/dictionary/right angle. Buy the book

Educator Resources

Cite this article as:

McAdams, David E. Right Angle. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/r/rightangle.html.

Image Credits

Revision History

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.)

All Math Words Encyclopedia is a service of Life is a Story Problem LLC.
Copyright © 2018 Life is a Story Problem LLC. All rights reserved.
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License