Angles at Circumference & Centre

Below shows a circle, with centre O.
The points A, B, C and X are points on the circumference of the circle.

You can:

• shift the point O to change the position of the circle
• shift the point X to change the size of the circle
• shift the points A and B to change their positions and the length of the arc AB
• shift the point C to change its position

Instructions:

1. Adjust the position and the length of the arc AB.
2. Adjust the position of the point C.
3. Check all boxes.
4. Observe the angle subtended by the arc AB at the circumference (i.e. ∠ACB) and the angle subtended by the arc AB at the centre (i.e. ∠AOB).
5. Repeat steps 1 ~ 4 for other positions and lengths of the arc AB and the point C.

Note: To see the animation, check all boxes, then click on the "play" button (at bottom left).



Download the GeoGebra file: http://www.geogebratube.org/material/download/format/file/id/41085

Download the Worksheet: http://db.tt/2USPPMtV