A= │A│= cos 2 - (-sin 2 ) = cos 2 + (sin 2 ) = 1 ---------- (I) We know that A -1 = adj A = adj A [From I]

If A= then A -1 =?

│A│= cos² - (-sin²)

= cos² + (sin²)

= 1 ---------- (I)

We know that A^-1= adj A

= adj A [From I]