證concyclic有咩方法??

証明四點是concyclic points，有以下三個方法。
1. Converse of angles in same segment
If a line segment subtends equal angles at the other two points on the same side of it, then the four points are concyclic.

2. Opposite angles of qaudrilateral supplementary
If a pair of opposite angles of a quadrilateral are supplementary, then the four points are concyclic.

3. Exterior angle of quadrilateral equal
If the exterior angle of a quadrilateral is equal to the interior opposite angle, then the four points are concyclic.