Page 126 - Mathematics Coursebook

12.4 Constructing squares, rectangles and polygons

b Cm 1 2 3 4 5 6 7 8 First draw a base line of length 5 cm.

80
70
60 110 100
50 130 120 80 70 60 50 40
40 140
30 150 30 Use a protractor to measure 108° from the left-hand end of the base line
20 160 90 100 110 120 130 140 150 160 170 180
20
10 170 10 and mark it with a small point.
0 180 0
8
7
0
6
180
Draw the second side of the pentagon 5 cm long.
10
5
170
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160
4
30
150
3
40
140
2
50
130
60
120
0 10 160 20 150 30 40 0 110 70 Cm 1
180 170 140 50 100
130 100 110 120 130 140 150 160 170 180 90 80 70 60 50 40 30 20 10 80
60
120
70
110
Use the protractor again to measure 108° from the end of the second line.
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Mark it with a small point.
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60
50
40
30 20 10
0
108°
90 100 110 120 130 140 150 160 170 180
Cm 1 2 3 4 5 6 7 8
70 100 80
60 110
50 130 120 80 70 60 50 40 Draw the third side of the pentagon 5 cm long.
40 140
30 150 90 100 110 120 130 140 150 160 170 180
30
20 160 20
10 170 10
0 180 0
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7
6
0
180
10
170
5
20
160
4
30
150
Use the protractor again to measure 108° from the end of the third line.
3
40
140
2
130
50
Cm 1
0 10 170 160 20 150 30 40 0 110 70 120 60 Mark it with a small point.
180 140 50 100
100 110 120 130 140 150 160 170 180 90 80 70 60 50 40 30 20 10 80
130
60 110 70 100 80 80 70
120
Cm 1 2 3 4 5 6 7 8 0 30 20 10 40 50 90 100 110 120 130 140 150 160 170 180 60
108°
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60 110 100 Draw the fourth side of the pentagon 5 cm long.
50 130 120 80 70 60 50 40
40 140
30 150 90 100 110 120 130 140 150 160 170 180
30
20 160 20
10 170 10
180 0
0
8
7
0
6
180
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170
5
20
160
4
30
150
3
140
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2 Join the end of the fourth side to the end of the base line to complete the
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130
10 20 30 120 60
0 160 150 40 0 110 70 Cm 1
180 170 140 50
130 120 60 110 70 100 110 120 130 140 150 160 170 180 90 80 70 60 50 40 30 20 10 100 80 pentagon.
80
Check that the fi fth side is 5 cm long.
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80
Check that the angle is 108°.
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50
40
30 20 10
0
108°
90 100 110 120 130 140 150 160 170 180
12 Constructions 125