Exterior Angle

Pronunciation: /ɪkˈstɪər i ər ˈæŋ gəl/ ?

1. Figure 1: Exterior angle

   The exterior angle of a polygon is made by extending one of the sides at a vertex, then taking the angle between the extended side and side of the polygon.[1][2] Note that the sum of the measure of an interior angle of a polygon and the measure of the corresponding exterior angle is 180° or π radians.

2. Figure 2: Interior angle between parallel lines.

   When two parallel lines are intersected by a third line called a transversal, the angles on the outside of the parallel lines are the exterior angles. Note that the sum of the measure of the exterior angle and the measure of the corresponding interior angle is 180° or π radians.

References

1. exterior angle. merriam-webster.com. Encyclopedia Britannica. (Accessed: 2010-01-24). http://www.merriam-webster.com/dictionary/exterior angle.
2. Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid, pp 8,28-29. Casey, John, LL.D. F.R.S.. Hodges, Figgis & Co., 1890. (Accessed: 2010-01-02). http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/8/mode/1up/search/exterior.
3. Stöcker, K.H.. The Elements of Constructive Geometry, Inductively Presented, pg 18. Translated by Noetling, William. Silver, Burdett & Company, 1897. (Accessed: 2009-12-28). http://www.archive.org/stream/elementsofconstr00noetrich#page/18/mode/1up.

More Information

• McAdams, David. Polygon. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem.org. 2009-03-12. http://www.allmathwords.org/article.aspx?lang=en&id=Polygon.

Printed Resources

Cite this article as:

Exterior Angle. 2009-12-21. All Math Words Encyclopedia. Life is a Story Problem.org. http://www.allmathwords.org/en/e/exteriorangle.html.

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• All images and manipulatives are by David McAdams unless otherwise stated. All images by David McAdams are Copyright © Life is a Story Problem.org and are licensed under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

Revision History

2009-12-23: Added "References" (McAdams, David.)
2008-06-07: Corrected spelling (McAdams, David.)
2008-06-04: Initial version (McAdams, David.)