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

माना \(f ( x )=\overrightarrow{ a } \cdot(\overrightarrow{ b } \times \overrightarrow{ c })\) का स्थानीय उच्चिष्ठ \(x _{0}\) है, जहाँ \(\vec{a}=x \hat{i}-2 \hat{j}+3 \hat{k}, \quad \vec{b}=-2 \hat{i}+x \hat{j}-\hat{k} \quad\) तथा \(\overrightarrow{ c }=7 \hat{ i }-2 \hat{ j }+ x \hat{ k }\) है। तब \(x = x _{0}\) पर \(\overrightarrow{ a } \cdot \overrightarrow{ b }+\overrightarrow{ b } \cdot \overrightarrow{ c }+\overrightarrow{ c } \cdot \overrightarrow{ a }\) का मान होगा

  1. A \(-30\)
  2. B \(14\)
  3. C \(-4\)
  4. D \(-22\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(-22\)

Step-by-step Solution

Detailed explanation

\(f(x)=\vec{a} \cdot(\vec{b} \times \vec{c})=\left|\begin{array}{ccc}x & -2 & 3 \\ -2 & x & -1 \\ 7 & -2 & x\end{array}\right|=x^{3}-27 x+26\) \(f^{\prime}(x)=3 x^{2}-27=0 \Rightarrow x=\pm 3\) and \(f ^{\prime \prime}(-3)<0\) \(\Rightarrow\) local maxima at \(x=x_{0}=-3\) Thus,…
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