8.3 – Methods of proving triangles similar
Ways to prove triangles congruent
Ways to prove triangles similar

vs.
Think about it: Always, Sometimes, Never
1.
2.
3.
4.
5.
If two triangles are similar, then they are congruent.
If two triangles are congruent, then they are similar.
If two triangles are obtuse then they are similar
If two triangles are equilateral, then they are similar.
Rectangles are similar
1-6) Decide if the information given in each diagram is enough to prove that the two triangles are similar. If there
is enough information, state why the triangles are similar and state which two triangles are similar.
B
1)
5
3
A
3
C
2)
X
Z
10
6
2
3) D
T
R
3
6
S
4
6
Y
B
A
K
9
F
F
4)
5)
30
C
4
A
6)
C
5
24
A
4
E
D
E
2
D
9
6
A3 B
D
C
J
H
18
4
B
C
4
E
8
B
D
1.
C
Given: ABCD is a parallelogram
Prove: BFE CFD
F
A
E
B
A
2.
Given:
DE || AB
Prove:
CDE
D
EF || AC
EFB
C
F
B
E
3. The sides of one triangle are 8, 14, and 12, and the sides of another triangle are 18, 21, and 12. Why are these
triangles similar?
O’
4. Given: ∆J’O’R’ is not a dilation of ∆JOR
Prove: O’R’ does not equal 40
O
25
8
5
25
J
6
R
J’
30
R’