[i]A, B, C [/i]and [i]D[/i] are points on the circumference of the circle. [br]An exterior angle is an angle outside of the cyclic quadrilateral, formed by extending one side of the quadrilateral. [br][br]Select one of the checkboxes, to show 1 of 2 possible exterior angles. [br]Move points [i]A, B, C[/i] and/or [i]D[/i] around to observe the relationship between the exterior angle and the interior opposite angle.