3.6Symmetry
Quick Answer
A figure has line symmetry if a line divides it into two mirror-image halves. A figure has rotational symmetry if it maps onto itself after a rotation of less than 360°. The order of rotational symmetry is the number of times the figure maps onto itself in a full rotation.
Essential Question
What does it mean for a figure to have line or rotational symmetry, and how do we identify the lines of symmetry and order of rotation?
Learning Goals
- 1Identify lines of symmetry in figures.
- 2Determine the number of lines of symmetry.
- 3Identify rotational symmetry and its angle.
- 4Determine the order of rotational symmetry.
Key Vocabulary
Line symmetry
A figure has line symmetry if a line divides it into two congruent mirror-image halves.
Line of symmetry
The line that divides a symmetric figure into two congruent halves.
Rotational symmetry
A figure has rotational symmetry if it maps onto itself after a rotation of less than 360°.
Order of rotational symmetry
The number of times a figure maps onto itself in a 360° rotation.
Full lesson content coming soon
Worked examples, guided practice problems, a workbook, quiz, and downloadable PDF resources will be added to this lesson in Phase 2. The learning goals and vocabulary above reflect the complete lesson scope.