If $\theta$ is the angle between the lines $AB$ and $CD$,then the projection of line segment $AB$ on line $CD$ is:

If $l_1, m_1, n_1$; $l_2, m_2, n_2$ and $l_3, m_3, n_3$ are the direction cosines of three mutually perpendicular lines,find the direction cosines of a line that makes equal angles with these lines.

If the direction ratios of two lines are $5, -12, 13$ and $-3, 4, 5$,then the angle between them is:

$A$ vector $v$ is equally inclined to the $x$-axis,$y$-axis,and $z$-axis respectively. Its direction cosines are:

The angle between the lines with direction ratios $(2, -2, 1)$ and $(1, -2, 2)$ is

If the projections of a line segment on the coordinate axes are $2, 3, 6$,find the length of the line segment.