Topics
10 . Shapes and position
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Australia
Year 4

10.06 Symmetry

Lesson
Practice
Lesson

Symmetry in different environments

Do you know what happens when we reflect a shape? The shape is mirrored across a fold or axis.

Can you see any symmetrical objects around you? Let's take a look at how we can check if a shape or object is symmetrical.

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Examples

Example 1

Which image has the line of symmetry drawn correctly?

A
A horizontal dashed line is drawn through the middle of a seashell. Ask your teacher for more information.
B
A diagonal dashed line is drawn through a seashell. Ask your teacher for more information.
C
A vertical dashed line is drawn down the side of a seashell. Ask your teacher for more information.
Worked Solution
Create a strategy

Choose the option that has been split into two identical halves that are the mirror image of each other.

Apply the idea

Only in option A can the shape be folded along the dashed line and lie on top of itself.

The answer is option A.

Idea summary

A line of symmetry splits an object into two identical halves that are the mirror image of each other.

The line of symmetry

This video takes a look at the line of symmetry, also called the axis of symmetry.

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Examples

Example 2

How many lines of symmetry does this painting have?

A circular pattern. Ask your teacher for more information.
Worked Solution
Create a strategy

Think of how many different lines can be drawn to split an object into two identical halves.

Apply the idea

Here is one of the lines of symmetry.

A diagonal dashed line is drawn through a circular pattern. Ask your teacher for more information.

Lines of symmetry can also be drawn horizontally, vertically, and diagonally the other way.

So there are 4 lines of symmetry.

Idea summary

If a shape is symmetrical, it means that when we draw a line through it, one side is identical to the other.

Some shapes or objects have more than one line of symmetry.

Outcomes

AC9M4SP03

recognise line and rotational symmetry of shapes and create symmetrical patterns and pictures, using dynamic geometric software where appropriate

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