Page 75 - MATHEMATICS COURSE FOR SECONDARY SCHOOLS BOOK 2

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ainer? h is a
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18 cm by 10 cm by 3 cm.
The ice-tray can hold 8 cubes of ice. Each ice-cube has edges of length 3 cm. Calculate:
4
M
The circle
E
The faces of all these objects are circular. Each face is in the shape of a circle.
A
S
U
REMENT (b) the capacity of the ice-tray
f an
(c) the volume of the ice-tray.
(a) the volu
me o
ice
-cub
e
Try this method.
Draw a straight line across
a sheet of paper. Mark
point A near one end. Hold
the compass on edge on S the paper, with the S pointer
directly above point A.
The cen
The ra
Any str circle t circle.
A radi centre
The rad How m
The di
The lo from o anothe diamet the circ
A diam passing meeting
The dia d. How
Activit
(a) Fin end
can, spra
(b) Roll part
wit thic Rem aro use mea
Thi leng
THE CIRCLE
N WE
11 12 1 10 2
93
84 765
NN
WE WE
SS
AB
of a
rium?
any hold?
edge
er?
cm by sc.
of that a
3 cm
What is a circle?
A circle is a path traced out by points that are all a constant distance from the centre point. The path is the circumference and the fixed distance is the radius.
What attributes of a circle are measurable?
􏰀 Its perimeter, diameter and radius are lengths.
􏰀 The amount of surface inside the perimeter is area.
The circumference of a circle
Assume that the only instrument you have available for measuring length is a wooden ruler. How could you find the perimeter of the circular face of a compass?
Roll the compass on its edge, along the
line, until the S pointer reaches its initial downward position, as in the diagram. Mark the new position of the S pointer on the line. Call this point B. The compass has made a complete turn. Measure the distance AB.
The distance AB is equal to the perimeter of the compass (a circle). The perimeter of the circle is called its circumference.
The circumference of a circle is the distance around the circle or the length of the boundary line of the circle. It is a special name given to the perimeter.
The circumference of a circle is usually denoted by the letter C.
Centre O Diameter
337
The centre of a circle
69 The point exactly at the middle of a circle is called its centre.
The centre of a circle is the point that is
o
t c
x a
e
a
m m
d
4 i
d
a o
T
u t
a
a
n n
r e
m m
y
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h k
u a
q idistanc from all points on th circ mf r nc
n
N WE S
c
n
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r
e
f
e
m
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cm
m
c
r
i
C
Radius