1. Advanced Geometry Similarity Lesson 1B
Dilations

2. CD = 15, r = 3 Example: Find the measure of the dilation image or the
pre-image of using the given scale factor.
CD = 15, r = 3
C'D' = 7, r =

3. Example:
Trapezoid EFGH has vertices E(-8, 4), F(-4, 8), G(8, 4),
and H(-4, -8). Find the image of trapezoid EFGH after
a dilation centered at the origin with a scale factor of
Graph the pre-image and the image.

4. To determine the scale factor of a dilation:
look at the coordinates of a point from the pre-image
and the corresponding point from the image
divide the image coordinate by the pre-image coordinate
Ex: D(8, -3) and D’(6, -2.25)
image = =
pre-image

5. Example:
Determine the scale factor used for each dilation with
center C. Determine whether the dilation is an
enlargement, reduction, or congruence transformation.

6. Example:
Jamie is using a photo editing program to reduce
posters that are 1 foot by 1.5 feet to 9 inch by 13.5 inch.
What scale factor did he use?

7. Example:
A 5-inch by 7-inch photograph has been enlarged by a
factor of 150%. What are the new dimensions of the
photograph?
How has the area of the preimage changed?

8. Example:
Find the perimeter of ΔABC.
Graph the image of ΔABC after a
dilation centered at the origin with
scale factor -2.
Find the perimeter of ΔA’B’C’ and
compare it to the perimeter of ΔABC.