Download The Aim of this lesson is to show you how to use a

Cabri Worksheet
Angles in the same segment etc.
South Hunsley School
Mathematics Department
The Aim of this lesson is to show you how to use a dynamic geometry
software package called Cabri Geometre. A dynamic geometry software
package allows you to do the sort of constructions you can do with a pencil,
ruler and compasses, but because it is ‘dynamic’, you can move parts of the
construction around to see what happens if things change.
Each section will guide you through a construction and then ask you some questions about
it. It is important that you always label any point that you draw. You may need to use the
‘Cabri Help Sheet’.
Construction
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Place a Point in the centre of the page.
Label The Point O.
Draw a Circle with Point O as the centre.
Place four Points on the Circle.
Label these Points A, B, C and D.
Draw line Segment AO. Draw line Segment OC.
Draw Segments AB, BC, AD and CD.
Mark Angle ABC. Mark Angle AOC. Mark Angle ADC.
Measure Angle ABC. Measure Angle AOC. Measure Angle ADC.
Your construction is now complete. You can move points A, B, C and D using
the Arrow tool.
Show your construction to your teacher and ask if you can print it. Now answer the
questions. You can write the answers on your printout.
1. What is the reflex angle AOC? (Write this on your construction).
2. What do you notice about the Angles?
3. Move Point B so that it is between Points A and D. What do you notice
about angles ABC and ADC?
Fact Time:
 The angle subtended by a chord at the centre of a circle is twice
the angle subtended by the chord at the circumference of the
circle.
 Angles subtended by a chord at the circumference of the circle in
the same segment are equal.
Can you make AC a diameter of the circle? What angle does this
make ABC? How does this show that the angle in a semicircle is 90°?