Triangle Similarity Test  All corresponding angles equal (AAA)
Definition: Triangles are similar if the measure of all three
interior angles in one triangle
are the same as the corresponding angles in the other.
This (AAA) is one of the three ways to test that two triangles are similar . For a list see
Similar Triangles.
Try this
Drag any orange dot at P,Q,R. The triangle LMN will change to remain similar to the left triangle PQR.
If all three angles in one triangle are the same as the corresponding angles in the other,
then the triangles are similar. So for example, in the triangle above the
interior angle
∠P is exactly equal
to the corresponding angle ∠L in the other triangle.
∠Q is equal to ∠M, and
∠R is equal to ∠N.
And so, because all three corresponding angles are equal, the triangles are similar.
Notice that the the three angles are drawn in a magenta color to indicate they
are the things being used to test for similarity.
What does this mean?
 Since all three corresponding angles are equal, we can be sure the triangles are similar.
 Because the triangles are similar,
this means that the three pairs of corresponding sides are in the same proportion to each other. (See Similar Triangles)
But don't forget
Similar triangles can be rotated and/or mirror images of each other (reflected).
(See Similar triangles.)
In the figure on the right, each angle in one triangle is equal to the corresponding angle in the other,
and so are still similar even though triangle is the mirror image of the other, rotated and bigger.
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Other similarity topics
Similar Polygons
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