The direction cosines of the line which bisects the angle between the positive direction of $Y$ and $Z$ axes are

If the relation between the direction ratios of two lines in $\mathbb{R}^3$ are given by $l+m+n=0$ and $2lm+2mn-ln=0$,then the angle between the lines is ($l, m, n$ have their usual meaning).

If the direction cosines of a line are $\frac{1}{c}, \frac{1}{c}, \frac{1}{c}$,then:

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?

The projections of a vector on the three coordinate axes are $6, -3, 2$ respectively. The direction cosines of the vector are . . . . . . .

If the line with direction ratios $(1, \alpha, \beta)$ is perpendicular to the line with direction ratios $(-1, 2, 1)$ and parallel to the line with direction ratios $(\alpha, 1, \beta)$,then $(\alpha, \beta)$ is