AngleAngle Similarity
Pronunciation: /ˈæŋ.gəl ˈæŋ.gəl ˌsɪm.ə'lær.ɪ.ti/ Explain
Abbreviation: AA Similarity
In Euclidean geometry,
two triangles are known to be
similar
if two corresponding
angles are congruent.^{[2]}
Two angles are congruent if they have the same measure. This is called
AA similarity.
AA stands for angle, angle.
If ΔA is similar to ΔB,
write "ΔA ∼ ΔB"
and say, "Triangle A is similar to triangle B."
In Euclidean geometry
the sum of the angles of a triangle is always 180° = 2π
rad.
This means that if two corresponding angles are congruent between two triangles, then the
third angle must also be congruent. This is sometimes called
AAA similarity
for angleangleangle similarity.
However, since AAA similarity is exactly the same thing as AA similarity, this term is
rarely used.
Click on the blue points and drag them to change the figure.
Angles A and A' are congruent and angles B and B' are congruent. When you change the figure, what does not change?

Manipulative 1  AngleAngle Similarity (AA Similarity) Created with GeoGebra. 
References
 McAdams, David E.. All Math Words Dictionary, AA similarity. 2nd Classroom edition 201501084799968. pg 8. Life is a Story Problem LLC. January 8, 2015. Buy the book
 Keller, Samuel Smith. Mathematics for Engineering Students, Plane and Solid Geometry. pg 83. www.archive.org. D. Van Nostrand Company. 1908. Last Accessed 6/12/2018. http://www.archive.org/stream/mathengineer00kellrich#page/83/mode/1up/search/Similarity. Buy the book
More Information
 Triangle similarity postulates/criteria. www.khanacademy.org. Kahn Academy. 6/19/2018. https://www.khanacademy.org/math/geometry/hsgeosimilarity/hsgeotrianglesimilarityintro/v/similaritypostulates.
 Euclid of Alexandria. Elements. Clark University. 9/6/2018. https://mathcs.clarku.edu/~djoyce/elements/elements.html.
Cite this article as:
McAdams, David E. AngleAngle Similarity. 4/12/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/a/aasimilarity.html.
Image Credits
Revision History
4/12/2019: Changed equations and expressions to new format. (
McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (
McAdams, David E.)
6/12/2018: Removed broken links, updated license, implemented new markup. (
McAdams, David E.)
1/4/2010: Added "References". (
McAdams, David E.)
9/16/2008: Change manipulative from Geometer's Sketchpad to Geogebra. (
McAdams, David E.)
9/3/2007: Added paragraph on AAA similarity. (
McAdams, David E.)
8/25/2007: Replaced graphic in figure 1 with manipulative. (
McAdams, David E.)
7/12/2007: Initial version. (
McAdams, David E.)