JEE Main & Advanced JEE Main Paper (Held On 8 April 2017)

  • question_answer
    The line of intersection of the planes \[\vec{r}.\left( 3\hat{i}-\hat{j}+\hat{k} \right)=1\]and\[\vec{r}.\left( \hat{i}+4\hat{j}-2\hat{k} \right)=2,\]is: [JEE Online 08-04-2017]

    A) \[\frac{x-\frac{6}{13}}{2}=\frac{y-\frac{5}{13}}{7}=\frac{z}{-13}\]

    B) \[\frac{x-\frac{7}{7}}{2}=\frac{y}{-7}=\frac{z+\frac{5}{7}}{13}\]

    C) \[\frac{x-\frac{6}{13}}{2}=\frac{y-\frac{5}{13}}{-7}=\frac{z}{-13}\]

    D) \[\frac{x-\frac{4}{7}}{-2}=\frac{y}{7}=\frac{z-\frac{5}{7}}{13}\]

    Correct Answer: C

    Solution :

                    \[\vec{n}={{\vec{n}}_{1}}\times {{\vec{n}}_{1}}\]                 \[\left| \begin{matrix}    {\hat{i}} & {\hat{j}} & {\hat{k}}  \\    3 & -1 & 1  \\    1 & 4 & -2  \\ \end{matrix} \right|\]                 \[=\hat{i}(-2)-\hat{j}(-7)+\hat{k}(13)\]                 \[\overline{n}=2\hat{i}+7\hat{j}+13\hat{k}\]                 Now                 \[3x-y+z=1\]                 \[x+4y-2z=2\]                 But z = 0                 \[3x-y=1\times 4\]                 \[x+4y=2\]                 \[13x=6\]             \[x=6/13\]           \[y=5/13\]?..is                                 \[\]                 or            \[\]        


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