Inverse Trigonometric Functions

If \(x \in \left( {0,{\pi \over 2}} \right)\), then the value of \({\cos ^{ - 1}}\left( {{7 \over 2}(1 + \cos 2x) + \sqrt {({{\sin }^2}x - 48{{\cos }^2}x)\sin x} } \right)\) is equal to