JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Morning)

  • question_answer
    The equation of the line passing through \[\left( -4,\text{ }3,\text{ }1 \right)\], parallel to the plane \[x+2y-z-5=0\] and intersecting the line\[\frac{x+1}{-3}\,\,\,=\,\,\,\frac{y-3}{2}\,\,=\,\,\frac{z-2}{-1}\] [JEE Main Online Paper (Held On 09-Jan-2019 Morning]

    A) \[\frac{x+4}{3}\,\,\,=\,\,\,\frac{y-3}{-1}\,\,=\,\,\frac{z-1}{1}\]

    B) \[\frac{x+4}{1}\,\,\,=\,\,\,\frac{y-3}{1}\,\,=\,\,\frac{z-1}{3}\]

    C) \[\frac{x+4}{-1}\,\,\,=\,\,\,\frac{y-3}{1}\,\,=\,\,\frac{z-1}{1}\]

    D) \[\frac{x-4}{2}\,\,\,=\,\,\,\frac{y-3}{1}\,\,=\,\,\frac{z+1}{4}\]

    Correct Answer: A

    Solution :

    The equation of required line passing through \[\left( -4,\text{ }3,\text{ }1 \right)\] is \[\frac{x+4}{a}\,\,=\,\,\frac{y-3}{b}\,\,=\,\,\frac{z-1}{c}\] given line is \[\frac{x+1}{-3}\,\,=\,\,\frac{y-3}{2}\,\,=\,\,\frac{z-2}{-1}\] Now the required line is parallel to plane x \[+\,2y-z-5=0\] \[\therefore \] given lines are coplanar \[\because \,\,\,\,\,\left| \begin{align}   & -3\,\,\,\,\,\,0\,\,\,\,\,\,\,\,1 \\  & a\,\,\,\,\,\,\,\,\,b\,\,\,\,\,\,\,c \\  & -3\,\,\,\,\,\,2\,\,\,\,\,-1 \\ \end{align} \right|\,\,\,\,\,\,\,=\,\,\,\,\,\,0\] \[3\left( -b+2c \right)+0+2a+3b=0\] \[-2a\,\,+\,\,6c\,\,=\,\,0\] \[\]??. (1) Also   \[a+2b-c=0\] \[3c+2b-c=0\]         [use (1)] \[2c\,\,+\,\,2b\,\,=\,\,0\] \[b\,\,=\,\,-c\] \[\therefore \] Required line is \[\frac{x+4}{(3c)}\,\,=\,\,\frac{y-3}{-c}\,\,=\,\,\frac{z-1}{c}\] \[\frac{x+4}{3}\,\,=\,\,\frac{y-3}{-1}\,\,=\,\,\frac{z-1}{1}\]


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