Topics
11. Shapes and angles
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Australia
Year 3

11.04 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.

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