Similarity and Congruence 16Nov09

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Similarity and Congruence 16-Nov-09
Understand the idea of similarity and
congruence Find an unknown sides on similar shapes
LEVEL 7
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In maths, the word CONGRUENT means that the
ANGLES are the SAME and the LENGHTS are the SAME.
EXACTLY THE SAME
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In maths, the word SIMILAR means that the ANGLES
are the same and the LENGHTS are DIRECTLY
PROPORTIONAL
Similarity is like pictures on two different
sized T.V. sets that are on the same channel
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Which triangles are i. Congruent ii. Similar?
B
C
A
D
E
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Which triangles are i. Congruent ii. Similar?
A
C
B
D
E
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Which parallelograms are i. Congruent ii.
Similar?
B
A
C
D
E
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Which trapeziums are i. Congruent ii. Similar?
A
B
C
E
D
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Which regular pentagons are i. Congruent ii.
Similar?
A
B
C
E
D
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Which regular hexagons are i. Congruent ii.
Similar?
B
A
C
E
D
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Here are two similar triangles. Find the lengths
A and B.
X 2
B
5
X 2
3
A
X 2
4
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Find the SCALE FACTOR that multiplies 4 to give
8 4 x 2 8 Now use this to get A and B A 6 and
B 10
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Here are two similar triangles. Find the lengths
A and B.
X 6
B
10
X 6
S
3
A
X 6
4.5
27
How did you get the x 6?
27 4.5 6
12
2
D
4.5
20
18
C
50
12.5
5
11
E
12.5
F
12
3.6
9
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A firm called Airfix used to make plastic models.
Here is a Bristol Bulldog model. The model and
the real plane are similar to scale.
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All measurements are in cm
Find the scale factor and the missing lengths
N
O
S
S. F. New Old New Old x S.F. Old New
S.F.
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All measurements are in cm
Scale factor 72
N
O
S
S. F. New Old New Old x S.F. Old New
S.F.
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