The perpendicular distance of the point $P(6, 7, 8)$ from the $XY$-plane is:

Consider the following statements:
Assertion $(A)$: The direction ratios of a line $L_1$ are $2, 5, 7$ and the direction ratios of another line $L_2$ are $\frac{4}{\sqrt{19}}, \frac{10}{\sqrt{19}}, \frac{14}{\sqrt{19}}$. Then the lines $L_1, L_2$ are parallel.
Reason $(R)$: If the direction ratios of a line $L_1$ are $a_1, b_1, c_1$, the direction ratios of a line $L_2$ are $a_2, b_2, c_2$ and $a_1 a_2 + b_1 b_2 + c_1 c_2 = 0$, then the lines $L_1, L_2$ are parallel. Which one of the following is true?

Find the direction cosines of the vector joining the points $A(1, 2, -3)$ and $B(-1, -2, 1)$,directed from $A$ to $B$.

If a line makes angles $\alpha, \beta, \gamma$ with the three-dimensional coordinate axes respectively,then $\cos 2\alpha + \cos 2\beta + \cos 2\gamma = $

What are the direction cosines of the line joining the points $(4, 3, -5)$ and $(-2, 1, -8)$?

If the direction cosines of two lines are given by $l+m+n=0$ and $l^2-5m^2+n^2=0$, then the angle between them is