Straight Angle

Pronunciation: /streɪt 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 straight angle is an angle that measures 1/2 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. D. Van Nostrand Company. 1908. Last Accessed 12/13/2018. Buy the book
  2. Hilbert, David. The Foundations of Geometry. pp 18-19. Translated by Townsend, E. J., Ph. D.. The Open Court Publishing Company. 1950. Last Accessed 12/13/2018. Buy the book

Cite this article as:

McAdams, David E. Straight Angle. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC.

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Revision History

12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)
12/10/2018: 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.)
5/5/2011: Initial version. (McAdams, David E.)

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