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Geometry/Similar Triangles
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For two triangles to be similar, all 3 corresponding angles must be congruent, and all three sides must be proportionally equal.
Two triangles are similar if...
Two angles of each triangle are congruent.
The acute angle of a right triangle is congruent to the acute angle of another right triangle.
The two triangles are congruent. Note here that congruency implies similarity.