Symmetry Cambridge IGCSE Mathematics (9–1) revision
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In plain words
A shape has line symmetry if you could fold it in half and the two halves match. It has rotational symmetry if it looks the same more than once as you turn it right round.
Three things to know
- A line of symmetry is a mirror line. A rectangle has 2, a square 4, an equilateral triangle 3, a circle infinitely many.
- The order of rotational symmetry is how many times the shape fits on to itself in one full turn. A square has order 4; a rectangle and a parallelogram have order 2.
- A regular polygon with n sides has n lines of symmetry and rotational symmetry of order n.
Tips and tricks
- A parallelogram has no lines of symmetry, though it looks as if it should. Try folding one.
- Every shape fits on itself after a full turn, so "order 1" means no rotational symmetry.
It lands in your notebook with its questions as flashcards.
Symmetry: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
How many lines of symmetry does a square have?
Two through the middles of the sides, and two diagonals.
What is the order of rotational symmetry of an equilateral triangle?
It fits on itself three times in a full turn.
How many lines of symmetry does a parallelogram have?
Folding along a diagonal doesn't make the halves match.
What is the order of rotational symmetry of a rectangle?
It looks the same after a half turn.
How many lines of symmetry does a regular pentagon have?
One through each corner.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 6 marks. Write your answers on paper, then check them.
Symmetry
Cambridge IGCSE Mathematics (9–1) 0980 · 6 marks · papermunch.org
Name ______________________________ Date ______________
State the number of lines of symmetry and the order of rotational symmetry of a rectangle.[2]
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2 lines of symmetry; order 2.
State the number of lines of symmetry and the order of rotational symmetry of a regular hexagon.[2]
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6 lines of symmetry; order 6.
State the number of lines of symmetry and the order of rotational symmetry of a parallelogram.[2]
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No lines of symmetry; order 2.
Answers: Symmetry
- 1. 2 lines of symmetry; order 2.
- 2. 6 lines of symmetry; order 6.
- 3. No lines of symmetry; order 2.