Investigating circle theorems

Activity 1: Finding the centre of the circle                        

You will need a cut-out paper circle (about 12cm diameter).

• Use a circle that does not show the centre.
• Fold your circle along a diameter. Mark the ends A and B.
• Now unfold your circle and then fold again along a different diameter and mark the ends C and D. Also mark the point where  AB and CD intersect as O. Why is this the centre?
• Is there another way of finding the centre?

Activity 2: Looking at the perpendicular bisector of a chord.

You will need a cut-out paper circle with centre O marked (about 12cm diameter).

• Fold over a segment of the circle to make a chord.  Mark the ends A and B.
• Fold the circle so that A and B come together. Unfold  and mark the points where this line cuts the circle as C and D.
• If AB and CD intersect at P, what do you know about AP and PB? What about angle CPA?
• How is CD related to AB?
• Is CD a diameter of the circle?

Click here to download the INVESTIGATING CIRCLE THEOREMS worksheet

Click here to download the INVESTIGATING CIRCLE THEOREMS Inclusion and Home Learning Guide.

Click here to download Notes for Teachers.