Class 9 | Chapter 10 | Circles | Theorem 10.11

If there exists a circle such that all four vertices of a quadrilateral passes through it, then it is known as cyclic quadrilateral. To prove this theorem the prerequisite is the proof of theorem 10.8 which states: “The angle subtended by an arc at the centre is double the angle subtended by it at any point on the remaining part of the circle.”