GR 9 3-5-2 LEARNERS
Page 1 of 2
NAME:
Gr 9
Date:
Time
½ hr.
CAPS
3-5 Construction of Geometric Figures Revise: bisecting an
Reference angle; constructing an angle of 45°
3-5-2 Bisecting an angle; constructing an angle of 45°
Topic
1.
Think First! [5 mins]
1.1
1.6
Draw an angle of 45° without using your protractor.
Give one way in which you could estimate 45°
Measure your angle and see how accurate you were.
Draw an angle of 45° using your protractor.
Give a fact about an angle of 45° based on something you already know.
How could you use this fact to draw an angle of exactly 45° without using your
protractor?
What is the meaning of the word bisect?
2.
Go ahead! [10 mins]
2.1.
2.2
2.3
2.4
2.5
Draw an acute angle naming the arms PW and OW.
Bisect the angle without using your protractor. Name the bisector WZ
Draw an obtuse angle naming the arms DY and KY.
Bisect the angle without using your protractor. Name the bisector YX
Use your protractor to check if your constructions are accurate.
3.
Check your work! [5 mins]
1.2
1.3
1.4
1.5
Measure your angles with a protractor to check they are the correct size. Remember that if
you bisect an angle, you cut it exactly in half so the two angles in each construction should
be exactly the same size. Make sure you have used the correct method.
4.
Got it?
Now that you know how to bisect an angle, use your skill to construct an angle of 45°. How
will you do this?
4.1
Using any one of the three methods you know, construct and angle of 90°
(or two lines perpendicular to one another)
4.2
Bisect one of the angles of 90°. How big is each of these two angles?
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GR 9 3-5-2 LEARNERS
Page 2 of 2
5.
Going further! [5 mins + own time]
5.1
5.2
5.3
5.5
Draw a triangle ABC with sides between 8cm, 10 cm and 12 cm.
Construct the bisectors of each angle of the triangle.
Mark the point where the bisectors cross M. Point M is a point of concurrency.
(Concurrency means coming together.)
Using your set square, draw lines from M to AB, BC and CA.
Name the lines MJ, MK and ML.
Measure MJ, MK and ML. What do you notice?
Use a radius with the same length as MJ/MK/ML. Draw a circle. What happens?
6.
Going even further! [own time]
6.1
Draw an obtuse angled triangle and do the same construction as in 4 above.
What happens?
6.2
Repeat for a right-angled triangle. What happens?
5.4
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www.e-classroom.co.za