In this illustration, instead of showing students the obvious symmetry properties of circle, the students are instead requested to prove themselves are the property. While some students are able to observe and prove effectively, most students may required scaffold from teacher:
1. Select "Show tangents from point C to circle", do you observe the two radius, OD and OE?
2. Select "Show line segment OC", are you able to spot two triangles, OCD and OCE?
3. Select " Show angle between tangents and angle bisector", prove that the line OC is indeed the angle bisector.
