Cyclic Quadrilaterals

[color=#ff0000][b]Definition:[/b][/color][br][br]A [color=#0000ff][b]cyclic quadrilateral[/b][/color], by definition, is [color=#0000ff]any quadrilateral that can be inscribed inside a circle.  That is, all 4 vertices of a cyclic quadrilateral always lie on the circle itself. [/color] [br][br]Mess around with the applet for a couple of minutes, and then answer the questions that follow.  [br]
Based upon your observations, [color=#ff0000][i]what can you conclude about both pairs of opposite angles of any cyclic quadrilateral?[/i][/color]  [br][br]Prove your assertion true using a theorem previously learned.  Explain fully why what you've observed in the applet above is true.   [br][br]

Information: Cyclic Quadrilaterals