# 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[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, right angle. 2nd Classroom edition 20150108-4799968. pg 157. 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 12/4/2018. http://www.archive.org/stream/mathengineer00kellrich#page/2/mode/1up/search/right. Buy the book
3. 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
4. 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

McAdams, David E. Right Angle. 5/3/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/r/rightangle.html.

### 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.)