Three particles P, Q and R are moving along the vectors $\overrightarrow A = \widehat i + \widehat j$, $\overrightarrow B = \widehat j + \widehat k$ and $\overrightarrow C = - \widehat i + \widehat j$ respectively. They strike on a point and start to move in different directions. Now particle P is moving normal to the plane which contains vector $\overrightarrow A$ and $\overrightarrow B$. Similarly particle Q is moving normal to the plane which contains vector $\overrightarrow A$ and $\overrightarrow C$. The angle between the direction of motion of P and Q is $${\cos ^{ - 1}}\left( {{1 \over {\sqrt x }}} \right)$$. Then the value of x is $\underline{\hspace{2cm}}$.