Acute Angle
Pronunciation: /əˈkyut ˈæŋ gəl/ ?
Figure 1: Acute angles measure < 90° 
 Manipulative 1: Classes of angles. Created
with GeoGebra. Click to see gadget full screen. 

Angles
are divided into four classes according to their measure. An acute angle
is an angle that measures less than 1/4 of a full
circle^{[1][2]}.
Click on the blue point in the manipulative and drag it to change the figure.

References
 acute angle. merriamwebster.com. Encyclopedia Britannica. (Accessed: 20091221). http://www.merriamwebster.com/dictionary/acute angle.
 Keller, Samuel Smith. Mathematics for Engineering Students, Plane and Solid Geometry, pg 2. D. Van Nostrand Company, 1908. (Accessed: 20100102). http://www.archive.org/stream/mathengineer00kellrich#page/2/mode/1up/search/acute.
 Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid, 10th Edition, pg 4. Casey, John, LL.D. F.R.S.. Hodges, Figgis & Co., 1890. (Accessed: 20100102). http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/4/mode/1up/search/acute.
Printed Resources
Cite this article as:
Acute Angle. 20100101. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/a/acuteangle.html.
Translations
Image Credits
Revision History
20100101: Added reference to Euclid's Elements, Expanded table of angle classes. (
McAdams, David.)
20080916: Changed text on classes of angles to a table. Changed images 2 and 3 to one manipulative (
McAdams, David.)
20080303: Revised other resources, added reference to radians (
McAdams, David.)
20070716: Expanded keyword 'acute' to include 'angle' (
McAdams, David.)
20070712: Initial version (
McAdams, David.)