**Prove that a cyclic parallelogram is a rectangle.**

**Solution:**

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)**

** (2) **

**(Sum of opposite angles of a cyclic quadrilateral is equal to )** ** **

Using equation** (1)** in equation **(2)**, we get

**(3)**

Therefore, ABCD is a parallelogram with which means that ABCD is a rectangle.