Unit 9 · Symmetry
Symmetry
Mathematics · Grade 7
What You Will Be Able To Do
🪞Find every line of symmetry in a shape, and prove it by folding
🔄Work out the order of rotational symmetry and the smallest angle of turn
⚖️Show that the two kinds of symmetry are completely independent
🏛️Explain why symmetry saves an architect or an engineer half their work
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Last unit, every transformation moved a shape somewhere new. Symmetry asks a different question: is there a transformation that leaves the shape looking exactly as it was?
Presenter notes: Open by connecting to the previous unit rather than starting fresh. Last week every transformation moved a shape somewhere new. Hold up a paper square, reflect it in a vertical line, and ask what changed. Nothing visible did, because the square landed exactly on itself. Then do the same with a paper letter F and it obviously changes. That contrast is the whole subject of this lesson: some shapes are unaffected by a transformation, and those are the symmetrical ones.