Chapter 7.2 Similar Polygons
Vocabulary
• Similar – Two polygons are similar if
– 1) Corresponding angles are congruent
– 2) Corresponding sides are proportional
~
stands for similar
Vocabulary
• Similarity ratio – the ratio of the lengths of
corresponding sides of similar figures
• Example:
AB BC CA


DE EF FD
A
B
D
C
E
ABC ~ DEF
F
Vocabulary
• Golden rectangle – rectangle that can be
divided into a square and a rectangle that is
similar to the original rectangle
D
F
C
ABCD is a rectangle
ADFE is a square
ABCD ~ BCFE
A
E
B
Vocabulary
• Golden ratio – the ratio of the length of a
golden rectangle to its width. The value of the
golden ratio is 1 5 or about 1.62
2
Determining Similarity
• Determine whether the triangles are similar.
If they are, write a similarity statement and
give the similarity ratio
B
20
A
E
15
16
24
C
D
12
18
F
• Given: Corresponding angles congruent
• Are the corresponding sides proportional?
AB

DE
BC

EF
AC

DF
Answer
• ABC ~ DEF with similarity ratio of
3
4
or 3:4
ABCD~EFGH complete each statement
B
C
mE 
53
D
A
F
G
127
AB AD

EF
E
H
LMNO~QRST
• Find the value of x
O
L
2
5
T
N
M
Q
X
6
S
R
Classwork/Homework
• Pgs 375-376 1-16, 21-28