The scale factor is
.
Solution:
<em>The scale factor of a dilation is the ratio of the length of the dilated i.e. transformed figure to the corresponding lengths of the original figure.</em>
ABC is the original triangle.
A'B'C' is the dilated triangle.
One side of ΔABC, AC = 18
Corresponding side of ΔA'B'C' = 9



Hence the scale factor is
.