Right Angle

Pronunciation: /raɪt ˈæŋ gəl/ Explain

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)
Manipulative 1: Classes of angles. Created with GeoGebra.
Click to see gadget full screen.

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

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


  1. Keller, Samuel Smith. Mathematics for Engineering Students, Plane and Solid Geometry. pg 2. www.archive.org. D. Van Nostrand Company. 1908. Last Accessed 1/2/2010. 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 1/2/2010. 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 3/12/2009. http://www.merriam-webster.com/dictionary/right angle.

Educator Resources

Cite this article as:

McAdams, David E. Right Angle. 5/5/2011. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/r/rightangle.html.

Image Credits

Revision History

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