Indirect Measurement
•
Similar triangles can be used to measure distances or
heights that are difficult to measure in a traditional
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way:
Indirect Measurement Using
Similar Triangles
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Monday – 2/28/11
Page 491
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Shadow Method
5 ft
32 ft
shadow of pole height of pole

shadow of bldg height of bldg
5 8

32 x
256  5 x
51.20  x
In the picture the angle of the
sun is the same in both
triangles and both triangles
have a right angle so they are
similar by AA Sim.
You can use the lengths of the
shadows and the height of the
pole to find the height of the
building.
The building is about 51.2 feet tall.
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One method uses shadows to create similar triangles.
Another method uses a reflection in a mirror to create
similar triangles.
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Mirror Method
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8 ft
1. Distances across rivers or canyons, or
2. Heights of tall objects that are awkward to measure.
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The angles of the reflection in
the mirror are the same so the
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triangles
are similar
by 0100
AA 1011
Sim.
You can use the distances on
the ground and the height of
the person to find the height of
the climbing wall.
height of person distance from mirror to person

height of wall
distance from mirror to wall
5 6.5

x 85
425  6.5 x
65.38 ft.  x
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The wall is about 65.38 feet tall.
Assignment #8
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Indirect Measurement Problems &
Pg. 494: 29, 32 – 34
Due Wednesday, 3/2/11
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