305. In a rectangular coordinate system $O x y z$, point $M$ has coordinates $x=-2, y=5, z=0$. Find the coordinates of its radius vector $\bar{r}=\overline{O M}$.
Solution. Abscissa $X=x=-2$, ordinate $Y=y=5$, applicate $Z=z=0$. Therefore, $\bar{r}=\{-2 ; 5 ; 0\}$.

Radius vector $\bar{r}$ lies in the plane $x O y$.