Geometry · Similarity & Right Triangles
AA Similarity
HSG-SRT.A.3
Definition
Two triangles are similar if two pairs of corresponding angles are congruent.
Examples
- If two angles of one triangle equal two angles of another, the triangles are similar by AA.
- Matching 40 and 60 degree angles in two triangles proves similarity by AA.
Key rule
Only two angle pairs are needed to prove triangle similarity — the third angle pair follows automatically.
Memory hook
Two matching angles is enough — the third takes care of itself.