JEE Main & Advanced Sample Paper JEE Main Sample Paper-1

  • question_answer
    A line segment has length 63 and direction ratios < 3, - 2, 6 >. If the line makes an obtuse angle with x -axis, then the components of the vector are

    A)  27, -18, 54                          

    B)  27,18, - 54

    C)  - 27,18, - 54       

    D)  27, -18, - 54

    Correct Answer: C

    Solution :

    Let components of line segment vector be a, b, c. \[\therefore \]\[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}={{(63)}^{2}}\]                                       ?(i) Also, \[\frac{a}{3}=-\frac{b}{2}=\frac{c}{6}=\lambda \]                                   (say) \[\Rightarrow \]\[a=3\lambda ,b=-2\lambda ,c=6\lambda \] From Eq. (i), \[9{{\lambda }^{2}}+4{{\lambda }^{2}}+36{{\lambda }^{2}}={{(63)}^{2}}\] \[\Rightarrow \]\[{{\lambda }^{2}}+81\Rightarrow \lambda =\pm 9\] Since, \[a=3\lambda <0\]as the line makes an obtuse angle with x-axis, \[\lambda =-9\]. \[\therefore \] Components are - 27,18, - 54.


You need to login to perform this action.
You will be redirected in 3 sec spinner