Properties of Cyclic Quadrilaterals
Enrichment #1 -
Explore the quadrilateral that has been inscribed in a circle.  Make a conjecture about the angles in the quadrilateral.  Attempt to prove your conjecture.
Hints:  
1.  Drag one of the vertices of the quadrilateral.  What do you notice that changes?
2.  Drag the the vertices to create the following shapes.   - Parallelogram, Rectangle, Square, Rhombus.  What happens to the intersection point of the diagonals?
Next - construct a general quadrilateral that is NOT inscribed in a circle.  Does the property you noticed about the angle measures still hold true?