MCQ
રેખાઓ $ \vec r \,\, = \,\,\left( {4\hat i\,\, - \,\,\hat j} \right)\,\, + \;\,\lambda \,\,\left( {\hat i\,\, + \,\,2\hat j\,\, - \,\,3\hat k} \right)\,\,$ અને $ \vec r \, = \left( {\hat i\,\, - \,\,\hat j\, + \,2\hat k} \right)\, + \,\,\mu \,\,\left( {2\hat i\,\, + \;\,4\hat j\,\, - \,\,5\hat k} \right)$ વચ્ચે ન્યુનતમ અંતર શોધો. 
  • A
    $\frac{{\sqrt 3 }}{2}$
  • B
    $\frac{{\sqrt 5 }}{3}$
  • C
    $\frac{2}{{\sqrt 3 }}$
  • $\frac{6}{{\sqrt 5 }}$

Answer

Correct option: D.
$\frac{6}{{\sqrt 5 }}$
d
આપણે જાણીએ છીયે કે રેખાઓ $\,_{\text{r}}^ \to \,\, = \,\,_{{a_1}}^ \to \, + \;\,\lambda _{{b_1}}^ \to $ અને $\,_r^ \to \,\, = \,\,_{{a_2}}^ \to \,\, + \;\,\mu _{{b_2}}^ \to $ વચ્ચે ન્યુનતમ અંતર :

$d\,\, = \,\,\left| {\frac{{\left( {_{{a_2}}^ \to \,\, - \,\,_{{a_1}}^ \to } \right).\,\,\left( {_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to } \right)}}{{|_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to |}}} \right|$

આપેલ સમીકરણો ને અનુક્રમે સમીકરણ $_r^ \to \,\, = \,\,_{{a_1}}^ \to \, + \,\,\lambda \,_{{b_1}}^ \to \,$ અને $_r^ \to \,\, = \,\,_{{a_2}}^ \to \,\, + \,\,\mu _{{b_2}}^ \to $ સાથે સરખાવતા 

$_{{a_1}}^ \to \,\, = \,\,4\hat i\,\,\, - \,\,\hat j,\,\,_{{a_2}}^ \to \,\, = \,\,\hat i\,\, - \,\,\hat j\,\, + \;\,2\hat k$

$_{{b_1}}^ \to \,\, = \,\,\,\hat i\,\,\, + \;\,2\hat j\,\, - \,\,3\hat k\,$ અને $\,_{{b_2}}^ \to \,\, = \,\,2\hat i\,\, + \;\,4\hat j\,\, - \,\,5\hat k$

$\therefore \,\,_{{a_2}}^ \to \,\, - \,\,_{{a_1}}^ \to \, = \,\, - \,\,3\hat i\,\, + \,\,0\hat j\,\, + \;\,2\hat k$ 

અને, $_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to \,\,\, = \,\,\left| {\begin{array}{*{20}{c}}
  {\hat i}&{\hat j}&{\hat k} \\ 
  1&2&{ - 3} \\ 
  2&4&{ - 5} 
\end{array}} \right|\,\, = \,\,2\hat i\,\,\, - \,\,\hat j\,\, + \;\,0\hat k$

$ \Rightarrow \,\,\left( {_{{a_2}}^ \to \,\, - \,\,_{{a_1}}^ \to } \right)\,\,.\,\,\left( {_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to } \right)\,\, = \,\,\left( { - 3\hat i\,\, + \;\,0\hat j\,\, + \;\,2\hat k} \right)\,\,.\,\,\left( {2\hat i\,\, - \,\,\hat j\,\, + \;\,0\hat k} \right)\,\, = \,\, - 6$

અને, $|_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to |\,\, = \,\,\sqrt {4\,\, + \;\,1\,\, + \;\,0} \,\, = \,\,\sqrt 5 $

$\therefore \,\,d\,\, = \,\,\left| {\frac{{\left( {_{{a_2}}^ \to \,\, - \,\,_{{a_1}}^ \to } \right).\,\,\left( {_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to } \right)}}{{|_{{b_1}}^ \to \,\, \times \,\,_{{b_2}}^ \to |}}} \right|\,\, = \,\,\left| {\frac{{ - 6}}{{\sqrt 5 }}} \right|\,\, = \,\,\frac{6}{{\sqrt 5 }}$

 

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