Q99 / 160 · AP EAMCET 2021 (23 Aug Shift 2) · Mathematics
If a line makes angles $90^{\circ}, 135^{\circ}$ and $45^{\circ}$ with the positive $X, Y$ and $Z$ axis respectively, then its direction cosines are
- A$\left(0, \frac{1}{2}, \frac{1}{\sqrt{2}}\right)$
- Correct answerB$\left(0, \frac{-1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right)$
- C$\left(1, \frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right)$
- D$\left(1, \frac{-1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right)$
Solution
Given, a line makes $90^{\circ}, 135^{\circ}$ and $45^{\circ}$ with the positive $x, y$ and $z$ axes respectively.
Hence, it's direction cosines are
$ < \cos 90^{\circ}, \cos 135^{\circ}, \cos 45^{\circ}>$
$=\left(0, \frac{-1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right)$
Hence, the correct answer is option: 'B'.