Similarity in shapes

I can recognise that similar shapes have sides in proportion to each other but angle sizes are preserved.

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Year 9

Similarity in shapes

I can recognise that similar shapes have sides in proportion to each other but angle sizes are preserved.

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Share activities with pupils

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Lesson details

Key learning points

Two shapes are not similar if there is a pair of lengths with a different multiplicative relationship.
Similar shapes are not always easy to spot visually.
A ratio table can help you find the scalar and functional multipliers in similar shapes.
The angle sizes do not change.

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.

Common misconception

Pupils may find it difficult to match up corresponding measurements on two congruent shapes when they are in different orientations.

Look lengths which are between any pairs of known angles or look for angles which are between pairs of adjacent known lengths. Also, tracing paper could be used to reflect/rotate/translate one shape onto the other.

To demonstrate that angles in a triangle can always be read in the same order (either by going clockwise or anticlockwise around the vertices) ask three pupils to stand in a triangle. Then ask them to try to rearrange their order so that they are not stood next to the same person.