Topics
12. Geometry
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AustraliaNSW
Stage 3

12.03 Properties of shapes

Lesson
Practice
Lesson

Are you ready?

Can you recall the names of common  2D shapes  ?

Examples

Example 1

What is the name of the shape below?

The image shows a rectangle.
A
Triangle
B
Rectangle
Worked Solution
Create a strategy

Think of a shape that has 2 pairs of opposite sides with equal lengths.

Apply the idea

From the option above, the shape that has 2 pairs of opposite sides with an equal length is a rectangle.

So the correct option is B: Rectangle

Idea summary

To help work out the name of a shape, think about properties like:

  • How many sides it has

  • What sides are the same length

Classify 2D shapes

This video will show you how to work out the name of a 2D shape based on its properties.

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Examples

Example 2

Which of the following shapes are rectangles? Choose all correct answers.

A
A 4 sided shape with 2 opposite pairs of equal sides and with right angles at each corner.
B
A 4 sided shape with all 4 sides equal. Opposite angles are equal.
C
A circle.
D
A 4 sided shape with 2 opposite pairs of equal sides and with right angles at each corner.
Worked Solution
Create a strategy

Look for shapes that have 4 sides with opposite sides equal, and 4 right-angles.

Apply the idea

Options A, B, and D all have 4 sides and opposite sides equal. But option B does not have right angles.

The rectangles are options A and D.

Idea summary

The features of 2D shapes help us know which shape we are looking at, such as:

  • the number of sides, including any that are equal or parallel

  • the number of angles, as well as any right angles.

Classify 3D shapes

This video will look at the properties of some 3D shapes including prisms and pyramids.

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Examples

Example 3

Here is a square pyramid:

A square pyramid.
a

How many faces does it have?

Worked Solution
Create a strategy

Faces are the flat sides of a solid object.

Apply the idea

It has 5 faces: the 4 triangles and the 1 square base.

b

How many vertices does it have?

Worked Solution
Create a strategy

Vertices are the corners where two edges meet.

Apply the idea

It has 5 vertices.

c

How many edges does it have?

Worked Solution
Create a strategy

An edge is where two faces meet.

Apply the idea

It has 8 edges.

Idea summary

The features of 3D shapes include:

  • the number of faces, and the shape of each face

  • the number of edges

  • the number of vertices

  • the shape of the base they have (for pyramids).

Outcomes

MA3-14MG

identifies three-dimensional objects, including prisms and pyramids, on the basis of their properties, and visualises, sketches and constructs them given drawings of different views

MA3-15MG

manipulates, classifies and draws two-dimensional shapes, including equilateral, isosceles and scalene triangles, and describes their properties

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