M4.4.3 For the adult
Enlargements
A shape is enlarged by scale factor 2 about a point. Where does a corner that is 3 squares right of the point go?
What this chapter teaches
An enlargement multiplies every distance from a centre by a scale factor. Lengths change and angles stay the same. A scale factor between 0 and 1 makes the shape smaller. The centre is where the lines through matching corners meet.
Three questions to ask
There is no one right wording. Listen for the idea.
- What two things do you need to describe an enlargement?
- What does a scale factor of one half do to a shape, and where does the image lie?
- How can you find the centre when you are given a shape and its image?
After the chapter, the learner can
- Enlarge a shape by a scale factor from a centre
- Enlarge a shape by a scale factor of 1/2
- Find the centre of an enlargement
What they copy into their notebook
Enlarge by multiplying each distance from the centre by the scale factor. Image = centre + factor × (corner − centre). Lines through matching corners meet at the centre.