Exterior Angle
Pronunciation: /ɪkˈstɪər i ər ˈæŋ gəl/ Explain
 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.


 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
 exterior angle. merriamwebster.com. Encyclopedia Britannica. MerriamWebster. Last Accessed 8/6/2018. http://www.merriamwebster.com/dictionary/exterior angle.
 Casey, John, LL.D., F.R.S.. The First Six Books of the Elements of Euclid. pp 8,2829. Translated by Casey, John, LL.D. F.R.S.. www.archive.org. Hodges, Figgis & Co.. 1890. Last Accessed 8/6/2018. http://www.archive.org/stream/firstsixbooksofe00caseuoft#page/8/mode/1up/search/exterior. Buy the book
 Stöcker, K.H.. The Elements of Constructive Geometry, Inductively Presented. pg 18. Translated by Noetling, William A.M, C.E.. www.archive.org. Silver, Burdett & Company. 1897. Last Accessed 8/6/2018. http://www.archive.org/stream/elementsofconstr00noetrich#page/18/mode/1up. Buy the book
More Information
 McAdams, David E.. Polygon. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 3/12/2009. http://www.allmathwords.org/en/p/polygon.html.
Cite this article as:
McAdams, David E. Exterior Angle. 7/9/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/e/exteriorangle.html.
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Revision History
7/5/2018: Removed broken links, updated license, implemented new markup, implemented new Geogebra protocol. (
McAdams, David E.)
12/23/2009: Added "References". (
McAdams, David E.)
6/7/2008: Corrected spelling. (
McAdams, David E.)
6/4/2008: Initial version. (
McAdams, David E.)