What you’ll learn
Identify reflection symmetry.
Key idea
Reflect the apex as well as the paired base points across each proposed line.
All vertex images must remain in the set; testing two points alone is insufficient and does not classify untested lines.
Worked example
Classify examples and non-examples for the concept 'Identify reflection symmetry'.
Triangle vertices A=(-5, 0), B=(1, 0), C=(-1, 4). Does reflection across x=-2 preserve the triangle? Classify with all-vertex evidence.
- Reflection across x=-2 exchanges base endpoints and sends apex C to (-3, 4); this image is absent, so the full set fails.
- Reflection across y=0 sends apex to (-1,-4), absent from the set; fixing A and B alone is insufficient.
Answer: No — x=-2 sends C to (-3, 4), which is not a vertex.
Quick Check
Classify examples and non-examples for the concept 'Identify reflection symmetry'.
Triangle vertices A=(-8, 0), B=(4, 0), C=(-2, 2). Does reflection across x=-2 preserve the triangle? Classify with all-vertex evidence.