Cambridge International Mathematics

Assumed Knowledge (Geometry and graphs) 7

a

1 line of symmetry

b

no lines of symmetry

c

2 lines of symmetry

ROTATIONAL SYMMETRY

A figure hasrotational symmetryif it can be mapped onto itself more than once

as it rotates through 360 oabout a point called thecentre of symmetry.

The flag of the Isle of Man features a symbol called atriskelion

which has rotational symmetry.

Every time you rotate the triskelion through 120 oit fits onto itself.

This is done 3 times to get back to the starting position. We say

that itsorderof rotational symmetry is 3.

The number of times an object will fit onto itself when rotated

through 360 o(one complete turn) is called itsorder of rotational

symmetry.

1 How many lines of symmetry do the following have?

abcd

efgh

ijkl

2

3 Draw a triangle which has:

a no lines of symmetry b one line of symmetry c three lines of symmetry.

DEMO

Which of the following

alphabet letters show line

symmetry?

EXERCISE D

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