Enlargements

1
Enlargements
Objectives To be able to Enlarge shapes given a
scale factor and centre of enlargement. Find
centres of enlargement
2
Scale factors and centres of enlargement
The size of an enlargement is described by its
scale factor.
For example, a scale factor of 2 means that the
new shape is twice the size of the original.
The position of the enlarged shape depends on the
centre of enlargement.
3
How do I enlarge a shape?
Enlarge triangle A with a scale factor of 3 and
centre of enlargement (2,1)
Draw lines from the centre of enlargement to each
vertex of your shape
Calculate the distance from the CoE to a vertex
and multiply it by the scale factor to find its
new position
Repeat for all the other vertices
Join up your new points to create your enlarged
shape
4
What if the centre of enlargement is inside the
shape?
Enlarge shape B with scale factor 2 and centre of
enlargement (6,6)
5
What about fractional scale factors?
Enlarge shape C by scale factor ½ and centre of
enlargement (10,1)
Each vertex on the enlarged shape is half the
distance from the CoE than its corresponding
vertex on the original shape.
Even though the shape gets smaller, its still
called an enlargement.
6
How do I find the centre of enlargement?
Join up the corresponding vertices and extend the
lines
The point where they all intersect is your centre
of enlargement
CoE (2,9)
What was the scale factor of enlargement?