Page 88 - MAT KS3 Y8 Cambridge CheckPoint

8.2 Identifying symmetry of 2D shapes

8.2 Identifying symmetry of 2D shapes
vertical line of symmetry
A 2D shape may have line symmetry and it
horizontal line of symmetry
may have rotational symmetry.
This rectangle has two lines of symmetry. One of the
lines of symmetry is horizontal, the other vertical.
You can use dashed lines to show lines of symmetry on a shape.
If you fold a shape along its lines of symmetry,
one half of the shape will fit exactly on top of the other half.
This rectangle also has rotational symmetry of order 2.
The order of rotational symmetry is the number of times a shape
looks the same as it is rotated through one full turn.

Worked example 8.2

For each of these shapes write down: i the number of lines of symmetry
ii the order of rotational symmetry.
a b

a i 2 lines of symmetry This shape has two diagonal lines of symmetry.
ii Order 2 rotational symmetry In one full turn the shape will look exactly the same
twice, once after rotating it 180° and again after 360°.
b i No lines of symmetry It is not possible to draw any lines of symmetry onto
this parallelogram.
ii Order 2 rotational symmetry In one full turn the parallelogram will look exactly the same twice,
once after rotating it 180° and again after 360°.

✦ Exercise 8.2

1 Copy each of these shapes and draw on the lines of symmetry.
a b c d

e f g h

i j k l

2 For each of the shapes in question 1, write down the order of rotational symmetry.

86 8 Shapes and geometric reasoning