Let $\mathrm{P}(\mathrm{x}, \mathrm{y}, \mathrm{z})$ be a point in the first octant, whose projection in the xy -plane is the point Q . Let $\mathrm{OP}=\gamma$; the angle between OQ and the positive x -axis be $\theta$; and the angle between OP and the positive z -axis be $\phi$, where $O$ is the origin. Then the distance of $P$ from the $x$-axis is