If the projections of a line segment on the coordinate axes are $3, 4,$ and $5$,then its length is:

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

The direction cosines of two lines are $\langle\frac{\sqrt{3}}{2}, \frac{1}{4}, \frac{\sqrt{3}}{4}\rangle$ and $\langle-\frac{\sqrt{3}}{2}, \frac{1}{4}, \frac{\sqrt{3}}{4}\rangle$. Then the angle between the lines is equal to (in $^{\circ}$)

$A$ point $(x, y, z)$ moves parallel to the $xy$-plane. Which of the three variables $x, y, z$ remains fixed?

If $l, m, n$ are the direction cosines of a line that is perpendicular to the lines having the direction ratios $1, 2, -1$ and $1, -2, 1$,then $(l+m+n)^2=$

If a line makes angles $90^{\circ}, 60^{\circ}$ and $\theta$ with $x, y$ and $z$ axes respectively,where $\theta$ is acute,then the value of $\theta$ is