Key Concepts: Symmetry

Line Symmetry

A figure has line symmetry if a reflection over a line maps the figure onto itself. The line is called the line of symmetry (or axis of symmetry).

Rotational Symmetry

A figure has rotational symmetry if a rotation of less than 360° maps the figure onto itself. The smallest such angle is the angle of rotational symmetry.

• The order of rotational symmetry = 360° ÷ (angle of rotational symmetry).
• A regular n-gon has rotational symmetry of order n and n lines of symmetry.

Point Symmetry

A figure has point symmetry if a 180° rotation maps it onto itself. This is rotational symmetry of order 2.