JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Line and Plane

  • question_answer
    The xy-plane divides the line joining the points (?1, 3, 4) and (2, ?5, 6) [RPET 2000]

    A)            Internally in the ratio 2 : 3        

    B)            Internally in the ratio 3 : 2

    C)            Externally in the ratio 2 : 3       

    D)            Externally in the ratio 3 : 2

    Correct Answer: C

    Solution :

                       Let xy-plane divides the line joining the points \[(-1,\,3,\,4)\] and \[(2,\,-5,\,6)\] in \[\lambda :1\]. Then, \[z=\frac{{{m}_{1}}{{z}_{2}}+{{m}_{2}}{{z}_{1}}}{{{m}_{1}}+{{m}_{2}}}\]Þ \[z=\frac{6\lambda +4}{\lambda +1}\]            For xy-plane, \[z=0\]                    \[\Rightarrow 0=\frac{6\lambda +4}{\lambda +1}\] \[\Rightarrow \lambda =-2/3=-2:3\]            Externally in the ratio 2 : 3.                          Trick : Ratio = \[\frac{-{{z}_{1}}}{{{z}_{2}}}\] = \[\frac{-4}{6}\] = \[\frac{-2}{3}\]                    Externally in the ratio 2 : 3.


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