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: |
$0, -\frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}$ $-\frac{1}{\sqrt{2}}, 0, \frac{1}{\sqrt{2}}$ $\frac{1}{\sqrt{2}}, 0, -\frac{1}{\sqrt{2}}$ $0, \frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}$ |
$0, -\frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}$ |
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 $\frac{1}{\sqrt{2}}$. |