JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Self Evaluation Test - Three Dimensional Geometry

  • question_answer
    Which one of the following planes is normal the plane \[3x+y+z=5?\]

    A) \[x+2y+z=6\]

    B) \[x-2y+z=6\]

    C) \[x+2y-z=6\]

    D) \[x-2y-z=6\]  

    Correct Answer: D

    Solution :

    [d] Direction cosines of the normal to the plane  \[3x+y+z=5\]are 3, 1, 1 Direction cosines of the normal to the plane \[x-2y-z=6\] are 1, -2, -1 Sum of the product of direction cosines \[=3\times 1+1\times (-2)+1\times (-1)=0\] Hence, normal to the two planes are perpendicular to each other. Therefore two planes are also perpendicular.


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