CIRCLES 2

1
CIRCLES 2
2
radius
circumference
centre
tangent
diameter
chord
3
area of circle
Area of red square


4r2
A
4
area of circle
Area of blue square


A
2r2
5
Lets look at the area inside a circle
6
Lets use a diagram to help


c
8r
6r
Explain why the statement must be true
7
A group of students measured the radius
estimated the area of five circles to see how
they were related. Here are their results
8
The equation of the curve is A 3.1r2
Here is their graph
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p x d
C pd
C 2pr
2 x p x r
A pr2
p x r x r
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This circle has a diameter of 20 cm.
Find the radius, circumference area of the
circle
20 cm
Use p 3.14
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d2
Radius
20 cm
20 2

10 cm

pd
circumference

p x 20


3.14 x 20
62.8 cm
pr2
area

3.14 x 10 x 10

314 cm2
12
Choose a problem
semicircle
sector
End
13
Calculate the perimeter and area of this
semicircle
Use p 3.14
12 m
14
Calculate the perimeter and area of this
semicircle
Use p 3.14
12 m
pr22
pd2
Perimeter
d
Area
3.14 x 12 x 6
(3.14 x 12) 24
37.68 24
3.14 x 12 x 6
61.68 m
226.08 m2
15
Calculate the perimeter and area of this sector
8 cm
Use p 3.14
60o
16
Calculate the perimeter and area of this sector
8 cm
Use p 3.14
60o
pr2 6
pd6
Perimeter
2r
Area
3.14 x 8 x 8 6
(3.14 x 16) 16 6
24.4 cm
34.5 cm2
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End