Symmetry groups of Euclidean figures
The symmetries of a figure S⊂ℝⁿ are the Euclidean isometries g with g(S)=S.
Key knowledge
The symmetries of a figure S⊂ℝⁿ are the Euclidean isometries g with g(S)=S. They form a subgroup under composition and act on the figure; an invariant is a property unchanged by all selected transformations. A regular convex n-gon, n≥3, has a dihedral group of n rotations and n reflections.
Conditions and scope
- A symmetry maps the whole figure onto itself, not merely into itself.
- The polygon here is planar; abstract dihedral presentations and enumeration do not classify all space or wallpaper groups.
Sources · 2
References
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Evidence and review
Proposition 3 isometry closure, printed page 67; the figure-stabilizer subgroup follows by applying identity/composition/inverse to g(S)=S. Conrad section 1 definition and Theorem 2.2 with counting/construction proof, printed pages 1–3, supply the polygon example.
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