If a line makes angles of $90^\circ, 135^\circ$ and $45^\circ$ with the $x, y$ and $z$ axes, respectively, then its direction cosines are:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → $0, -\frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}$ ##
Direction cosines of a line making angle $\alpha$ with X-axis, $\beta$ with Y-axis and $\gamma$ with Z-axis are $l, m, n$
$l = \cos \alpha, m = \cos \beta, n = \cos \gamma$
Here, $\alpha = 90^\circ, \beta = 135^\circ, \gamma = 45^\circ$
So, direction cosines are
$l = \cos 90^\circ = 0$
$m = \cos 135^\circ = \cos(90^\circ + 45^\circ)$
$= -\sin 45^\circ = -\frac{1}{\sqrt{2}}$
and $n = \cos 45^\circ = \frac{1}{\sqrt{2}}$
Therefore, direction cosines are $0, -\frac{1}{\sqrt{2}}$ and $\frac{1}{\sqrt{2}}$.