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JEE Mains · Maths · STD 12 - 10. vector algebra

Let \(\vec{a}=2 \hat{i}+\hat{j}-2 \hat{k}\) and \(\vec{b}=\hat{i}+\hat{j} .\) If \(\vec{c}\) is a vector such that \(\vec{a} \cdot \vec{c}=|\vec{c}|,|\vec{c}-\vec{a}|=2 \sqrt{2}\) and the angle between \((\vec{a} \times \vec{b})\) and \(\vec{c}\) is \(\frac{\pi}{6}\), then the value of \(|(\vec{a} \times \vec{b}) \times \vec{c}|\) is:

  1. A \(\frac{2}{3}\)
  2. B \(4\)
  3. C \(3\)
  4. D \(\frac{3}{2}\)
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Answer & Solution

Correct Answer

(D) \(\frac{3}{2}\)

Step-by-step Solution

Detailed explanation

\(|\vec{a}|=a ; \vec{a} \cdot \vec{c}=c\) \(\text { Now }|\vec{c}-\vec{a}|=2 \sqrt{2}\) \(\Rightarrow c^{2}+a^{2}-2 \vec{c} \cdot \vec{a}=8\) \(\Rightarrow c^{2}+9-2(c)=8\) \(\Rightarrow C^{2}-2 C+1=0 \Rightarrow C=1 \Rightarrow|\vec{c}|=1\) Also,…
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