# Sec. 8.3: Similar Polygons ```Geometry Warm-Up 1/13/11
1)
In a triangle, the ratio of the measures of
three sides is 3:4:5, and the perimeter is 42
feet. Find the measure of the longest side of
the triangle.
2)
A boxcar on a train has a length of 40 feet
and a width of 9 feet. A scale model is made
with a length of 16 inches. Find the width of
the model.
Sec. 7.2: Similar
Polygons
Geometry
January 13, 2011
Are the following similar?
Similar – same shape but different size
Similar Polygons
A
ABCD ~ GEFH

Polygons are
similar when
1)
2)
Their corresponding
angles are
congruent
Their corresponding
sides are
proportional
D
G
H
B
C
E
AB = BC = CD = AD
GE
EF
FH
GH
F
Ex. 1: Decide whether the figures
are similar. L
O
10.5
4
18
M
P
12
12
9
Q
N
Ex. 2: You have been asked to create a poster to
advertise a field trip to see the Liberty Bell. You
have a 3.5 inch by 5 inch photo that you want to
enlarge. You want the enlargement to be 16
inches wide. How long will it be?
5
X = 22.9 inches
The length of the enlargement will be
3.5
Scale Factor – the ratio of the lengths of two corresponding
sides of similar polygons
Ex. 3: Parallelogram ABCD is similar to
parallelogram GBEF. Find the value of y.
B
E
Y = 19.2
C
12
G
15
F
y
A
24
D
Homework

Page 392 (8 – 18 E; 22)
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