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CUET · MATHS · PYQ PAPER 2023

If \(\vec{a}+\lambda \vec{b}\) is perpendicular to \(\vec{c}\), where
\(\vec{a}=-\hat{i}+2 \hat{j}+\hat{k}, \vec{b}=3 \hat{i}+2 \hat{j}+\hat{k}\), and \(\vec{c}=\hat{i}-\hat{j}\),
then :

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

Answer & Solution

Correct Answer

(D) \(\lambda=3\)

Step-by-step Solution

Detailed explanation

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