# Acute Angle

Pronunciation: /əˈkjut ˈæŋ.gəl/ Explain

 Figure 1: Acute angles measure < 90°

 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 six classes according to their measure. An acute angle is an angle that measures less than 1/4 of a full circle[2][3].

Classes of Angles
Table 1: Classes of angles

### References

1. McAdams, David E.. All Math Words Dictionary, acute angle. 2nd Classroom edition 20150108-4799968. pg 10. 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 6/12/2018. http://www.archive.org/stream/mathengineer00kellrich#page/2/mode/1up/search/acute. Buy the book
3. Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid. 10th Edition. pg 4. www.archive.org. Hodges, Figgis & Co.. 1890. Last Accessed 6/12/2018. http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/4/mode/1up/search/acute. Buy the book

McAdams, David E. Acute Angle. 4/11/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/a/acuteangle.html.

### Revision History

4/11/2019: Changed equations and expressions to new format. (McAdams, David E.)