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CUET · MATHS · PYQ PAPER 2023

Unit vectors perpendicular to the plane of vectors \(\vec{a}=\hat{i}-\hat{j}-3 \hat{k}, \vec{b}=\hat{i}+3 \hat{j}-\hat{k}\) are:

  1. A \(\pm \frac{-5 \hat{i}+\hat{j}+2 \hat{k}}{\sqrt{30}}\)
  2. B \(\pm \frac{5 \hat{i}+\hat{j}-2 \hat{k}}{\sqrt{30}}\)
  3. C \(\pm \frac{5 \hat{i}-\hat{j}+2 \hat{k}}{\sqrt{30}}\)
  4. D \(\pm \frac{-5 \hat{i}-\hat{j}-2 \hat{k}}{\sqrt{30}}\)
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Answer & Solution

Correct Answer

(C) \(\pm \frac{5 \hat{i}-\hat{j}+2 \hat{k}}{\sqrt{30}}\)

Step-by-step Solution

Detailed explanation

\(\vec{a} \times \vec{b} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 1 & -1 & -3 \\ 1 & 3 & -1 \end{vmatrix} = \hat{i}(1+9) - \hat{j}(-1+3) + \hat{k}(3+1)\) \(\vec{a} \times \vec{b} = 10\hat{i} - 2\hat{j} + 4\hat{k}\) Let \(\vec{c} = 5\hat{i} - \hat{j} + 2\hat{k}\) (by…
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