Prove that a cyclic parallelogram is a rectangle.
It is given that parallelogram ABCD is cyclic. We need to prove that ABCD is a rectangle.
(Opposite angles of a parallelogram are equal) (1)
(Sum of opposite angles of a cyclic quadrilateral is equal to )
Using equation (1) in equation (2), we get
Therefore, ABCD is a parallelogram with which means that ABCD is a rectangle.