Similar triangles: proportions
Two figures that have the same shape are similar
∆ABC is similar to ∆DEF
∡A≅∡
Similar figures have CONGRUENT angles
∆ABC is similar to ∆DEF
∡B≅∡
∡C≅∡
                       In similar figures,
corresponding (matching) sides are proportional
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
(enter each 2 segment letters in alphabetical order)
∆ABC is similar to ∆EFG
A
AB
=
B
C
BC
U
=
AC
V
W
These ∆s are similar, which means
they have proportional sides
12
x
12
9
=
x
6
G
These ∆s are similar, which means
they have proportional sides
12
x
12
9
=
9
6
x =
x
6
G
A
D
B
E
C
Segment DE
  is parallel
to segment AC
A
D
B
E
C
The parallel lines
form corresponding ∡s
∡BDE   ≅ ∡
∡BED  ≅ ∡
(One-letter angles)
A
∆ABC is similar to ∆
D
B
E
C
Segment DE
  is parallel
to segment AC
Since the ∆s have
2 corresponding
congruent angles,
they are SIMILAR.
A
∆ABC is similar to ∆ DBE
D
B
E
C
Segment DE
  is parallel
to segment AC
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