Chapter 20 · ICSE Class 8 Mathematics

Symmetry

Deepen your understanding of symmetry by combining line and rotational symmetry, and exploring symmetry in real-world designs.

🪞 Chapter 20

A shape with rotational symmetry of order 4 A pinwheel-like shape made of four identical blades arranged around a centre point, which looks the same after every quarter turn, giving it rotational symmetry of order 4 Order 4: looks the same every 90° turn
20.1

Shapes with Both Line and Rotational Symmetry

Many shapes have both types of symmetry at once. A regular polygon with n sides always has n lines of symmetry and rotational symmetry of order n.

1

A regular hexagon has how many lines of symmetry, and what order of rotational symmetry?

6 lines of symmetry, and rotational symmetry of order 6

2

Does a rectangle (not a square) have rotational symmetry? If so, what order?

Yes, order 2 — it looks the same after a 180° rotation

20.2

Symmetry in Real-World Designs

Symmetry appears throughout nature, architecture, and logos. Recognizing the type and order of symmetry in a design helps analyze how it was constructed.

1

A wheel with 8 evenly spaced spokes has what order of rotational symmetry?

8, since rotating by 45° (360°÷8) brings it back to looking the same

2

Why do many company logos use rotational symmetry rather than only line symmetry?

Rotational symmetry often looks more dynamic and modern, and works well when a logo needs to look balanced from multiple angles

Practice

Exercises

1. A regular octagon has how many lines of symmetry, and what order of rotational symmetry?

2. Does an equilateral triangle have both line and rotational symmetry?

3. A wheel with 6 evenly spaced spokes has what order of rotational symmetry?

4. Does a parallelogram (that isn't a rectangle or rhombus) have any line symmetry?

5. A regular pentagon has how many lines of symmetry?