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TRANSCRIPT
Subject : Mathematics
Topic : Geometrical Construction
Form : Two
Duration : 45 minutes
Learning Objective: Constructions Using a Straight Edge and a Pair of Compasses
Learning Outcomes :
At the end of lesson, students should be able to
• Construct the angle of 60 and 120 • Construct bisector of an angle.
Prerequisite knowledge :Students have already know • Construct a line segment of given length.• Construct a triangle given the length of the sides.• Construct a perpendicular to a line.
The perpendicular bisector of a given line segment. The perpendicular to a line through a point on the line. The perpendicular to a line passing through a point not on the line.
Approach : Constructive Learning
A
4. Then, label point C at the 60 mark using the outer scale. Remove the protractor. Join BC.
Draw the angle of 60 using the protractor
B
C
60
1. Draw a line AB.2. Place the base line of the protractor on AB.3. Place the centre of the protractor on the point B.5. An angle of 60 is drawn.ABC = 60
Construct an angle of 60°
Construct ABC = 60°
B C
A
60°
(a) Draw a straight line and mark the point B.(b) With B as the centre, use a compass to draw a big arc to cut the line at C.
(c) With the same radius and with C as the centre, cut the first arc at A.
(d) Join A to B. ABC = 60°
LMN = 60° PQR = 60° P
60°
L
60°
Draw a line AB of 5 cm. Construct an angle of 60° at A.
A B
60°
5 cm
Construct an angle of 120°
Construct BAD = 120°
A B
C
120°
D
BAD = 120° (a)Draw a straight line and mark the point A.(b) With A as the centre, use a compass to draw a big arc to cut the line at B.(c) With the same radius and with B as the centre, cut the first arc at C.(d) With the same radius and with C as the centre,
cut the second arc at D.(e) Join A to D.
Construct an angle of 120°
Construct ABD = 120°
B C
A
60°
D
120°
(a)Draw a straight line and mark the point B.(b) With B as the centre, use a compass to draw a big arc to cut the line at C.
(c) With the same radius and with C as the centre, cut the first arc at A.
(d)Join A to B.(e)Mark the point D at the other side of the line.ABD = 120°
Draw a line PQ of 6 cm. Construct an angle of 120° at Q.
P Q
60°
6 cm
XYZ = 120° MLN = 120°
Z
120°Z
120°
120°
Construct the bisector of an angle
Construct the bisector of ABC.
B
A
C
P
Q
R
(a) With B as the centre, use a compass to draw arcs to cut AB and BC at P and Q.(b) Without changing the radius and with P and then Q as the
centre, draw arcs to cut at R.
(c) Join R to B. BR is the bisector of ABC.
Construct an angle of 30°
Construct an angle of 60°
30°
then construct the angle bisector.
Construct an angle of 45°
Construct an angle of 90°
45°
then construct the angle bisector.
15°
15°
22 °
22.5°
2
1
150°
30°150°
75°
C
120°
D