$\displaystyle P$, $\displaystyle Q$ and $\displaystyle R$ are three points in space with coordinates $\displaystyle (2, -1, 4)$ , $\displaystyle (3, 1, 2)$ and $\displaystyle (-1, 2, 5)$ respectively. Find angle $\displaystyle Q$ in the triangle $\displaystyle PQR$.