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CUET · MATHS · PYQ PAPER 2025

If \(\hat{a}\) is a unit vector perpendicular to both the vectors \(\vec{b}=\hat{j}+2 \hat{k}\) and \(\vec{c}=\hat{i}+2 \hat{j}\), then \(\hat{a}\) is equal to :

  1. A \(\frac{-4 \hat{i}+2 \hat{j}+\hat{k}}{\sqrt{21}}\)
  2. B \(\frac{4 \hat{i}+2 \hat{j}-\hat{k}}{\sqrt{21}}\)
  3. C \(\frac{-4 \hat{i}+2 \hat{j}-\hat{k}}{\sqrt{21}}\)
  4. D \(\frac{-4 \hat{i}-2 \hat{j}-\hat{k}}{\sqrt{21}}\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(\frac{-4 \hat{i}+2 \hat{j}-\hat{k}}{\sqrt{21}}\)

Step-by-step Solution

Detailed explanation

\( \vec{b} \times \vec{c} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 0 & 1 & 2 \\ 1 & 2 & 0 \end{vmatrix} = \hat{i}(0-4) - \hat{j}(0-2) + \hat{k}(0-1) = -4\hat{i} + 2\hat{j} - \hat{k} \)…
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