Lines of Symmetry (Cambridge (CIE) IGCSE International Maths)

Revision Note

Lines of Symmetry

What is line symmetry?

  • Line symmetry refers to shapes that can have mirror lines added to them

    • Each side of the line of symmetry is a reflection of the other side

  • Lines of symmetry can be thought of as a folding line too

    • Folding a shape along a line of symmetry results in the two parts sitting exactly on top of each other

Lines of symmetry in isosceles triangles, squares, and rectangles
  • It can help to look at shapes from different angles; turn the page to do this

rotating a shape to see lines of symmetry
  • Some questions will provide a portion of a shape and a line of symmetry, and you need to fill in the remaining half of the shape

  • Be careful with diagonal lines of symmetry

    • Use tracing paper to trace the shape and then flip along the line of symmetry

  • Two-wayreflections (like part c below) occur if the line of symmetry passes through the shape

Examples of reflecting in a line of symmetry
Examples of reflecting in a line of symmetry
Symm Notes fig1, downloadable IGCSE & GCSE Maths revision notes

Exam Tip

  • It can help to add the lines of symmetry to a diagram if one is given in a question

  • You should be provided with tracing paper in the exam, use this to help you

    • You can request it if you are not given it at the start

Worked Example

Consider the shape below.

Symmetry worked example question

(a) Write down the number of lines of symmetry.

 The only line of symmetry is shown below

Symmetry worked example solution a

There is 1 line of symmetry. 

(b) Shade exactly 4 more squares so that the shape has 4 lines of symmetry.

The shape below has a horizontal, a vertical, and 2 diagonal lines of symmetry  

Symmetry worked example solution b

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Jamie Wood

Author: Jamie Wood

Jamie graduated in 2014 from the University of Bristol with a degree in Electronic and Communications Engineering. He has worked as a teacher for 8 years, in secondary schools and in further education; teaching GCSE and A Level. He is passionate about helping students fulfil their potential through easy-to-use resources and high-quality questions and solutions.