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140
ANSWERS
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170
ANSWERS
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60
ANSWERS
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40
ANSWERS
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30
ANSWERS
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55
ANSWERS
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45
ANSWERS
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80
ANSWERS
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540
ANSWERS
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Circumference and circle
Objective: after this lesson you will be able
to calculate the length of a circumference
to calculate the area of a circle
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Can you remember the names for these elements?
Circumference(the red line)
Centre
Radius
Diameter(its length is two times
the radius)
Chord
Arc
(the blue line)
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Circumferences is the perimeter of this shape
Try to measure some circumferences.
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Blue
PurpleYellow
Green
Red
Diameter
d
Circumference
C
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This is a special number:
= 3.141592653589793238462643383279502
You need to remember just
= 3.14
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To know the length of this circumference
you need to know
its diameter d.
The length of the
circumference isC=
So, the length of this circumference is:
C= = 3.14 12 = 37.68 ( 2 . . )
12 cm
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Calculate the length of this circumference
20 cm
Answer: 62.8 cmHint: C=
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Calculate the length of this circumference
15 cm
Answer: 47.1 cmHint: C=
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Calculate the length of this circumference
3 m
Answer: 18.84 mHint: C=
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Calculate the length of this circumference
5 mm
Answer: 31.4 mmHint: C=
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The area inside a circumference is called circle
Try to measure some circles.
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Blue
Purple
Yellow
Green
Red
Radius
r
Circle
C
r
Radius squared
r
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Again the special number:
= 3.14
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To know the area of this circle
you need to know
its radius r.
The area of the
circle is
=
So, the area of this circle is:
= = 3.14 12 = 452.16 (to 2 d.p.)
12 cm
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Calculate the area of this circle
15 cm
Answer: 706.5
Hint:A=
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Calculate the area of this circle
6.5 cm
Answer: 132.66
Hint:A=
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Calculate the area of this circle
18 cm
Answer: 254.34
Hint:A=
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Calculate the area of this circle
2.5 cm
Answer: 4.91
Hint:A=
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Calculate the length of the blue arc of
circumference
20 cm
Answer: 31.4 cm
C=
2 0 == 62.8 cm
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Calculate the length of the blue arc of
circumference
11 cm
Answer: 17.27 cmHint: C=
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Calculate the area of this semicircle
Answer: 2.45
2.5 cm
Hint:A=
W k h
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Worksheet