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

Cabri Worksheet
Cyclic quadrilateral
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 Polygon ABCD. (Remember to click on A to finish).
Mark Angle ABC. Mark Angle CDA.
Measure Angle ABC. Measure Angle CDA.
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 do you notice when you add up the Angles?
2. Is this the same if you move the Points around?
3. What happens to the Angles if you move the Points so that you don’t have a
quadrilateral, but have two triangles instead?
Fact Time:
 A quadrilateral whose vertices all lie on a circle is called a cyclic
quadrilateral
 The opposite angles in a cyclic quadrilateral always add up to 180°
Can you make your angles 90°? Now draw the line Segment AC,
What do you notice?