Symmetries of Polygons: Rotations and Reflections

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Geometry › Symmetries of Polygons: Rotations and Reflections

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1

Which symmetries does the polygon have? Consider rotations about the polygon’s center and reflections across lines in the plane.

Rotational symmetry of order 2 and exactly 2 reflection lines

Rotational symmetry of order 4 and 4 reflection lines

No rotational symmetry less than $360^\circ$ and no reflection lines

Rotational symmetry of order 8 and 8 reflection lines

Explanation

This question asks about the symmetries of a regular octagon. A symmetry is a transformation that maps the polygon onto itself. Regular octagons have extensive symmetry properties due to their 8 equal sides and angles. The octagon has rotational symmetry of order 8, meaning it maps onto itself under rotations of 45°, 90°, 135°, 180°, 225°, 270°, and 315° about its center. Additionally, it has exactly 8 lines of reflection symmetry: 4 lines connecting opposite vertices and 4 lines connecting midpoints of opposite sides. These symmetries make the regular octagon one of the most symmetric polygons. Students might think it has only 4 lines (like a square) or forget to count all rotational positions. To find all symmetries of regular polygons, remember that an n-sided regular polygon has n rotational symmetries and n reflection lines.