# Straight Angle

Pronunciation: /streɪt 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 span class="keyword">straight angle is an angle that measures 1/2 of a full circle.[2]

Classes of Angles
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

1. McAdams, David E.. All Math Words Dictionary, straight angle. 2nd Classroom edition 20150108-4799968. pg 171. Life is a Story Problem LLC. January 8, 2015. Buy the book
2. Keller, Samuel Smith. Mathematics for Engineering Students, Plane and Solid Geometry. pg 2. www.archive.org. D. Van Nostrand Company. 1908. Last Accessed 12/13/2018. http://www.archive.org/stream/mathengineer00kellrich#page/2/mode/1up/search/straight. Buy the book
3. 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. http://www.gutenberg.org/files/17384/17384-pdf.pdf. Buy the book

McAdams, David E. Straight Angle. 5/7/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/s/straightangle.html.

### Revision History

5/7/2019: Changed equations and expressions to new format. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)