in a cyclic quadrilateral, opposite angles are supplementary. if a pair of angles are supplementary, that me and they add up to 180 degrees. so if you have any quadrilateral inscribed in a circle, you can use that tot figure out the angle measures.
C obtuse po ata but I'm not sure about that
Conjecture (Quadrilateral Sum ): Opposite angles in any quadrilateral inscribed in a circle are supplements of each other.
not all two opposite right-angle quadrilaterals are rectangles.