Diapositiva 1

1
Circumference and Area of Circles
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The circumference of a circle is
the distance around a circle
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First we must define some things about a circle.
The radius is the distance from
the center of a circle to any point
on a circle.
Hint I like to define it as halfway through!
4
The diameter is the distance across a circle
through the center.
Hint The distance all the way across!
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We use Pi as the measurement to help us
find the circumference of a circle.
Pi, not Pie!
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Hint Pi 3.14
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Circumference Formulas
4in.
(pi x diameter)
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When the radius of a circle is given, the
following formula should be used.
Hint Always round your answers to the nearest
tenth.
31.4cm
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NOWLets have some fun.
Tell me what formula would be used to solve the
next five problems.
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C 2 x 3.14 x r
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C 3.14 d
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C 2 x 3.14 x r
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C 3.14 d
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C 2 x 3.14 x r
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Now that we have determined the correct formula
for each, lets work the problems.
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C 2 x 3.14 x r
C 2 x 3.14 x 3
The answer is 18.8in
17
C 3.14 d
C 3.14 x 8ft
The answer is 25.1ft
18
C 2 x 3.14 x r
C 2 x 3.14 x 122
The answer is 766.2mm
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C 3.14 d
C 3.14 x 17.5 cm
The answer is 55 cm
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Area of a Circle Formula
(pi x radius squared)
Area 50.24 in2
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Area of a Circle
(pi x radius squared)
Area 452.16 m2
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Area of a Circle
(pi x radius squared)
Area 254.34 cm.2
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Area of a Circle
Radius is ½ the diameter
Radius is 15 ft
(pi x radius squared)
Area 706.5 ft. 2
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Area of a Circle
Radius is ½ the diameter
Radius is 15 ft
(pi x radius squared)
Area 706.5 ft. 2
25
Area of a Circle
Radius is ½ the diameter
Radius is 7.5km
(pi x radius squared)
Area 176.6 km2