Circle: Cyclic Quadrilaterals

Cyclic Quadrilaterals The quadrilateral ABCD is inscribed in the circle. What to do: Click on the "Show interior angles" checkbox to display the interior angles at each vertex of the quadrilateral. Click and drag points A, B, C, and D to move them around. What is the sum of angles ABC and ADC? What is the sum of the angles DAB and DCB? What hypothesis can you make about the sum of opposite angles in a cyclic quadrilateral?