J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    The shortest distance between the straight line \[\frac{x-6}{1}=\frac{2-y}{2}=\frac{z-2}{2}\] and \[\frac{x+4}{3}-\frac{y}{-2}=\frac{1-z}{2}\] is

    A)  \[9\]             

    B)  \[\frac{19}{3}\]

    C)  \[\frac{16}{3}\]

    D)  \[4\]

    E)  None of these

    Correct Answer: E

    Solution :

    Given lines can be rewritten as \[\frac{x-6}{1}=\frac{y-2}{-2}=\frac{z-2}{2}\] and \[\frac{x+4}{3}=\frac{y}{-2}=\frac{z-1}{-2}\] Here,   \[{{x}_{1}}=6,\,\,{{y}_{1}}=2,\,{{z}_{1}}=2\] \[{{x}_{2}}=-4,{{y}_{2}}=0,\,{{z}_{2}}=1\] \[{{l}_{1}}=1,\,{{m}_{1}}=-2,\,{{n}_{1}}=2\] and \[{{l}_{2}}=3,\,{{m}_{2}}=-2,\,{{n}_{2}}=-2\] Now, \[\left| \begin{matrix}    {{x}_{2}}-{{x}_{1}} & {{y}_{2}}-{{y}_{1}} & {{z}_{2}}-{{z}_{1}}  \\    {{l}_{1}} & {{m}_{1}} & {{n}_{1}}  \\    {{l}_{2}} & {{m}_{2}} & {{n}_{2}}  \\ \end{matrix} \right|\] \[=\left| \begin{matrix}    -10 & -2 & -1  \\    1 & -2 & 2  \\    3 & -2 & -2  \\ \end{matrix} \right|\] \[=-10(4+4)+2(-2-6)-1(-2+6)\] \[=-100\] and \[\sqrt{\begin{align}   & {{({{m}_{1}}{{n}_{2}}-{{m}_{2}}{{n}_{1}})}^{2}}+{{({{n}_{2}}{{l}_{2}}-{{l}_{1}}{{n}_{2}})}^{2}} \\  & +{{({{l}_{1}}{{m}_{2}}-{{l}_{2}}{{m}_{1}})}^{2}} \\ \end{align}}\] \[=\sqrt{{{(4+4)}^{2}}+{{(6+2)}^{2}}+{{(-2+6)}^{2}}}\] \[=\sqrt{64+64+16}=12\] \[\therefore \]   Required shortest distance \[=\frac{-100}{12}=\frac{25}{3}\] [neglect \[(-ve)\] sign]


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