सदिश \(\left( {\vec i + \lambda \vec j + 3\vec k} \right)\)और \(\left( {3\vec i + 2\vec j + 9\vec k} \right)\)में λ का मान क्या है जो समानांतर है?

  1. \(\frac{2}{3}\)
  2. \(\frac{3}{4}\)
  3. \(\frac{5}{2}\)
  4. \(\frac{1}{2}\)

Answer (Detailed Solution Below)

Option 1 : \(\frac{2}{3}\)
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दिए गए दो सदिश समानांतर है, इसलिए इन दो सदिश का सदिश गुणनखंड शून्य होगा।

\(\vec a\parallel \vec b \Leftrightarrow \vec a \times \vec b = \vec 0\)

\(\Rightarrow \left| {\begin{array}{*{20}{c}} {\hat i}&{\hat j}&{\hat k}\\ 1&\lambda &3\\ 3&2&9 \end{array}} \right| = 0\)

\(= \left( {9\lambda - 6} \right)\hat i - \left( {9 - 9} \right)\hat j + \left({2 - 3\lambda} \right)\hat k = \vec 0\)

⇒ 9λ – 6 = 0 और 2 - 3λ = 0

∴ λ = 2/3
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