The object is the starting figure before a transformation has been applied.

The image is the resulting figure after a transformation has been applied.

Two shapes are similar if the only difference between them is their size. Their side lengths are in the same proportions.

Scale factor is the multiplier between similar shapes that describes how large one shape is compared to the other.

A property of a shape is invariant if that property has not changed after the shape is transformed.

Checking understanding of similarity

Maths

In this unit, pupils continued to build on their understanding of congruence and similarity with right-angled triangles. In the future unit, similarity is used to extend a right-angled triangle in the unit circle to any other right-angled triangle.

In the prior unit, pupils explored the effects of different transformations and whether the transformed shape was congruent or similar to the original shape. This is built on in this unit where pupils formalise the criteria for determining congruence in triangles and study rotational symmetry.

Geometrical properties: similarity and Pythagoras' theorem

A property of a shape is {{}} if that property has not changed after the shape is transformed.

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.

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

A parallelogram is enlarged by a scale factor of 3. Which of the following measurements will remain invariant?

The two triangles are similar. The value of $$x$$ is {{ }}.

A triangle has a base of 6 m and height of 2 m. A similar triangle, in the same orientation, has a base of 15 feet. Its height is {{}} feet.

Two shapes are {{}} if the only difference between them is their size. Their side lengths are in the same proportions.

The __________ is the multiplier between similar shapes that describes how large one shape is compared to the other.

Which rectangle is a correct enlargement of of rectangle R?

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 square has length 8 cm. It is enlarged by a scale factor of $$1\over{2}$$. The side length of its image is {{}} cm.

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 {{}}°.

This lesson will be removed by end of Summer Term 2025.

Checking understanding of similarity

Lesson outcome

This lesson will be removed by end of Summer Term 2025.