AAA similarity criterion
If three angles of one triangle are respectively equal to three angles of another triangle, the triangles are similar.
Practice This ConceptMain explanation
Teacher explanation
The third angle automatically matches because the angle sum of a triangle is 180°. So once two corresponding angles are equal, the full shape pattern is fixed.
Example
If one triangle has angles 35°, 75°, 70° and another triangle has the same angle pattern, the triangles are similar by AAA.
Simple analogy
Three equal angles, one same shape.
Common confusion
Students sometimes wait for side lengths even after all the corresponding angles have already matched.
Exam tip
If two corresponding angles match, the third one will also match because the total is always 180°.
Answer writing and exam use
1-mark use
Write the exact meaning of aaa similarity criterion in one clean line.
2-mark use
Define aaa similarity criterion and add one example or condition.
3-mark use
Explain aaa similarity criterion, show the method or example, and mention the common mistake.
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