SAS similarity criterion
Two triangles are similar if one included angle is equal and the two sides around that angle are proportional.
Practice This ConceptMain explanation
Teacher explanation
The included angle fixes the opening, and the two surrounding side ratios fix the scale. Together they are enough to match the triangles exactly in shape.
Example
If ∠A = ∠P and AB/PQ = AC/PR = 2/3, then triangles ABC and PQR are similar.
Simple analogy
Angle in the middle, sides on both sides.
Common confusion
Students often compare the wrong pair of sides or forget that the angle must lie between the compared sides.
Exam tip
Check the angle that lies between the two sides you are comparing.
Answer writing and exam use
1-mark use
Write the exact meaning of sas similarity criterion in one clean line.
2-mark use
Define sas similarity criterion and add one example or condition.
3-mark use
Explain sas similarity criterion, show the method or example, and mention the common mistake.
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