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

  • question_answer
    The vector \[\vec{a}=\alpha \hat{i}+2\hat{j}+\beta \hat{k}\] lies in the plane of the vectors \[\vec{b}=\hat{i}+\hat{j}\] and \[\vec{c}=\hat{j}+\hat{k}\] and bisects the angle between \[\vec{b}\] and\[\vec{c}\]. Then which one of the following gives possible values of a and b?

    A) \[\alpha =2,\beta =2\]

    B) \[\alpha =1,\beta =2\]

    C) \[\alpha =2,\beta =1\]

    D) \[\alpha =2,\beta =1\]

    Correct Answer: D

    Solution :

    [d] \[\therefore \vec{a}\] lies in the plane of \[\vec{b}\] and \[\vec{c}\] \[\therefore \vec{a}=\vec{b}+\lambda \vec{c}\] \[\Rightarrow \alpha \hat{i}+2\hat{j}+\beta \hat{k}=\hat{i}+\hat{j}+\lambda (\hat{j}+\hat{k})\] \[\Rightarrow \alpha =1,2=1+\lambda ,\beta =\lambda \Rightarrow \alpha =1,\beta =1\]


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