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- Year 9
Checking understanding of similarity
I can enlarge a shape and can state what changes and what is invariant.
- Year 9
Checking understanding of similarity
I can enlarge a shape and can state what changes and what is invariant.
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Lesson details
Key learning points
- An enlargement means a change in size.
- The lengths of the lines may change when enlarged.
- The angles inside an object do not change when enlarged.
- When an object is enlarged, the image is similar.
Keywords
Object - The object is the starting figure before a transformation has been applied.
Image - The image is the resulting figure after a transformation has been applied.
Similar - Two shapes are similar if the only difference between them is their size. Their side lengths are in the same proportions.
Scale factor - Scale factor is the multiplier between similar shapes that describes how large one shape is compared to the other.
Invariant - A property of a shape is invariant if that property has not changed after the shape is transformed.
Common misconception
When a pair of similar shapes are not in the same orientation, pupils may select an incorrect pair of lengths to calculate the scale factor.
Encourage pupils to take a systematic approach to locating pairs of corresponding lengths by looking for the longest edge in each shape, then the second longest, third longest, etc.
To help you plan your year 9 maths lesson on: Checking understanding of similarity, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Checking understanding of similarity, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
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The assessment exit quiz will test your pupils' understanding of the key learning points.
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Explore more key stage 3 maths lessons from the Geometrical properties: similarity and Pythagoras' theorem unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Licence
Prior knowledge starter quiz
6 Questions
Q1.Two shapes are if the only difference between them is their size. Their side lengths are in the same proportions.
Q2.The __________ is the multiplier between similar shapes that describes how large one shape is compared to the other.
Q3.Which rectangle is a correct enlargement of of rectangle R?

Q4.Triangle A has been enlarged by a scale factor of 2 to get triangle B. Match each unknown length from triangle B with its size.

$$a\text{ }$$ cm -
8 cm
$$b\text{ }$$ cm -
6 cm
$$c\text{ }$$ cm -
10 cm
Q5.A square has length 8 cm. It is enlarged by a scale factor of $$1\over{2}$$. The side length of its image is cm.
Q6.Each angle in an equilateral triangle is 60°. If an equilateral triangle is enlarged by a scale factor of 2, each of its angles will be °.
Assessment exit quiz
6 Questions
Q1.A property of a shape is if that property has not changed after the shape is transformed.
Q2.A shape is being enlarged by a scale factor of 4. One vertex is 3 cm from the centre of enlargement. Its corresponding vertex on the image will be cm from the centre of enlargement.

Q3.Sofia is enlarging the shape by a scale factor of 2. Which vertex has Sofia plotted incorrectly?

Q4.A parallelogram is enlarged by a scale factor of 3. Which of the following measurements will remain invariant?
Q5.The two triangles are similar. The value of $$x$$ is .
