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Angle in a semi-circle

Investigate the circle property by clicking and dragging any of the blue points. What observation can you make regarding the angle in a semi-circle? Confirm your conjecture by revealing the relevant measurements then show the property.

  1. What is the special name given to the chord AB?
  2. What type of angle is <AOB?
  3. This property can be proved using another circle property. What property is this?