Problem 11 · 1989 AJHSME
Hard
Geometry & Measurement
reflection-symmetry
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Answer: B — B.
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Hint 1 of 3
A mirror on a vertical line only swaps left and right — top stays top, bottom stays bottom. So track each feature's left/right side and leave its height alone.
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Hint 2 of 3
Two anchors pin down the mirror image: where the little corner square lands, and which way the slanted arms lean. Check both before choosing.
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Hint 3 of 3
The corner square sits at the TOP of the original, so it must stay at the top — that instantly throws out any choice with the square at the bottom, narrowing the field fast.
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Approach: swap left↔right, keep top/bottom, then match two anchors
- Reflection across the vertical dashed line is a left-right flip only: every feature keeps its height but trades sides. So the corner square stays at the top and moves to the opposite side, and the slanted arms reverse their lean.
- Use the corner square as the first filter — it's at the top in the original, so any choice with it at the bottom is out. Then check the arm lean against the mirror. Only B matches both anchors: square at the same top level on the flipped side, with the arms leaning the mirrored way.
- Why this transfers: to test a mirror image, don't eyeball the whole picture — pick one or two distinctive features (a corner mark, a lean direction) and verify each obeys the flip. Symmetry problems crack quickly once you reduce them to a couple of checkable anchors.
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