Enlarging a shape by a scale factor from a centre of enlargement. Every point on the shape moves away from (or towards) the centre by the same ratio.
To enlarge a shape:
- Draw rays from the centre of enlargement through each vertex
- Multiply each distance from the centre by the scale factor
- Mark the new vertices along those rays
Example: Scale factor 3 means each vertex ends up 3× as far from the centre as before.
Fractional scale factors (e.g. $\frac{1}{2}$) make the shape smaller — it's still called an enlargement even though the image is reduced.
Negative scale factors (Higher): the image appears on the opposite side of the centre and is rotated 180°. Scale factor $-2$ means the image is twice the size but flipped through the centre.
Two shapes are similar if one is an enlargement of the other — corresponding angles are equal and corresponding sides are in the same ratio.
Common error: measuring distances from the wrong point. The scale factor applies from the centre of enlargement, not from the shape itself.