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 answer
    B
    $\left(0, \frac{-1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right)$
  • 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'.

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