Similar Triangles and Proportions
Two figures that have the same shape 
but not necessarily the same size are similar.
∆ABC is similar to ∆DEF
Classify the two shapes shown in the diagram. 
congruent only
similar only
neither congruent nor similar
both congruent and similar
Similar figures have CONGRUENT corresponding angles
∡A≅∡
∆ABC is similar to ∆DEF
∡B≅∡
∡C≅∡
In similar figures, corresponding sides areproportional.
6
3
=
10
??
Complete the statement of proportionality
12
12
24
?
8
=
10
10
20
?
=
24
16
16
?
8
20
∆ABC is similar to ∆EFG
A
AB
EF
?
=
B
C
BC
FG
?
E
=
AC
EG
?
F
G
∆ABC is similar to ∆UVW
A
UV
?
AB
=
B
C
BC
VW
?
U
=
UW
?
AC
V
W
These ∆s are similar, which means
they have proportional sides
12
x
12
8
=
x
10
These ∆s are similar, which means
they have proportional sides
12
x
12
8
=
10
8
x =
x
10
Dilations on the Coordinate Plane Result in Similar Figures!
What is the scale factor if ABCD is dilated over the origin?
Scale Factor:
Given triangle DEF before a dilation centered at the originwith a scale factor of 5
What are the coordinates of point D' after the dilation?
D' (       ,       )
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