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CUET · MATHS · PYQ PAPER 2023

If \(\vec{a}=2 \hat{i}-\hat{j}+\hat{k}, \vec{b}=\hat{i}+\hat{j}-2 \hat{k}, \vec{c}=\hat{i}+3 \hat{j}-\hat{k}\), such that \(\vec{a}\) is perpendicular to \((\lambda \vec{b}+\vec{c})\), then the value of \(\lambda\) is :

  1. A 2
  2. B 3
  3. C \(-3\)
  4. D \(-2\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(-2\)

Step-by-step Solution

Detailed explanation

\(\vec{a} \cdot (\lambda \vec{b}+\vec{c}) = 0\) \((2 \hat{i}-\hat{j}+\hat{k}) \cdot ((\lambda+1) \hat{i} + (\lambda+3) \hat{j} + (-2\lambda-1) \hat{k}) = 0\) \(2(\lambda+1) - 1(\lambda+3) + 1(-2\lambda-1) = 0\) \(2\lambda+2 - \lambda-3 - 2\lambda-1 = 0\) \(-\lambda - 2 = 0\)…
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