If a line has direction ratios$2, -1, -2,$ determine its direction cosines.

Write the direction cosines of the line joining the points $(1, 0, 0)$ and $(0, 1, 1)$.

Show that the line joining the origin to the point $(2, 1, 1)$ is perpendicular to the line determined by the points $(3, 5, - 1) \mathrm{and} (4, 3, - 1)$.

For what value of p will the line through $(4, 1, 2) \mathrm{and} (5, p, 0)$ be perpendicular to the line through $(2, 1, 1) \mathrm{and} (3, 3, - 1)$

Find the values of p and q so that the line joining the points $(7, p, 2) \mathrm{and} (q, - 2, 5)$may be parallel to the line joining the points $(2, -3, 5) \mathrm{and} (-6, -15, 11).$