Given,\\\\(ABCD\\\\) is a cyclic parallelogram.To prove,\\\\(ABCD\\\\) is a rectangle.Proof:\\\\(∠1 + ∠2 = 180°\\\\) ...Opposite angles of a cyclic parallelogramAlso, Opposite angles of a cyclic parallelogram are equal.Thus,\\\\(∠1 = ∠2\\\\)\\\\(⇒ ∠1 + ∠1 = 180°\\\\)\\\\(⇒ ∠1 = 90°\\\\)One of the interior angle of the parallelogram is right angled. Thus, \\\\(ABCD\\\\) is a rectangle.