J20

Enlargements
Enlargement is described by stating the centre of enlargement and the scale factor. The
enlargement scale factor can be negative or positive.
image distance from centre
The ratio
is called the scale factor.
object distance from centre
Example
Triangle ABC is such that A(2, 1), B(4, 1) and C(3, 4) are its vertices. Find the
coordinates of its image after an enlargement with centre (0, 0) and scale factor:
(a) 2 (b) -2.
Solution
(a)
(b)
When the triangle is enlarged about (0, 0) with scale factor of 2, the coordinates of
the images are A 1(4, 2), B 1(8, 2) and C 1(6, 8).
When the triangle is enlarged about (0, 0) with scale factor of -2, the coordinates of
the image are A 2(-4, -2), B 2(-8, -2) and C 2(-6, -8).
Under an enlargement, an object and its image are similar but not congruent..