3/7/2017
Prebell
Words to Know (p. 81)
• Dilation - a transformation in which a figure is
made larger or smaller with respect to a point
called the center of dilation
• Enlargement – dilation that
creates a larger image
• Reduction – dilation that creates a smaller
image
• Scale factor – ratio of corresponding side
lengths of the image to the original figure
WB p. 20 # 7
82
Congruent & Similar Figures Venn
Diagram
CONGRUENT
FIGURES
SIMILAR
FIGURES
A rectangle has vertices 𝑊(−4, −6),
𝑋(−4, 8), 𝑌(4, 8), 𝑍(4, −6). Find its
vertices after a dilation with a scale factor
of ½. Identify the type of dilation.
To dilate a figure (with respect to the
origin):
• Multiply the coordinates of each vertex by the
scale factor.
• If the scale factor is > 1, the dilation is an
enlargement.
• If the scale factor is < 1, the dilation is a
reduction.
• If the scale factor is = 1,
the images are congruent!
Draw the figure and its image after a
dilation with the given scale factor.
Identify the type of dilation.
𝐴 1,1 , 𝐵 1,4 , 𝐶 3, 1 ; 𝑘 = 3
y
14
12
10
8
6
4
2
2
4
6
8
10
12
14
x
1
3/7/2017
Draw the figure and its image after a
dilation with the given scale factor.
Identify the type of dilation.
𝐺 −2, −2 , 𝐻 −2,6 , 𝐽 2,6 ; 𝑘 = 0.25
4
4
• Ex: 𝐷 5, 2 → 𝐷ʹ 2, 5
2
–4
–2
• To find scale factor:
– Divide an image coordinate (prime) by its original
coordinate.
y
6
–6
Scale Factor
2
4
6 x
–2
• 𝐸(11, 14) → 𝐸ʹ(38.5, 49)
–4
–6
Write a rule to describe the transformation.
𝑁(−4, 1), 𝑇(−5, 3), 𝐽(−4, 3), 𝐶 −1, 0
to
𝑁′(−1, 0.25), 𝑇′(−1.25, 0.75), 𝐽′(−1, 0.75),
𝐶′(−0.25, 0)
The blue figure is a dilation of the red
figure. Identify the type of dilation
and find the scale factor.
The blue figure is a dilation of the red
figure. Identify the type of dilation
and find the scale factor.
2