JEE Main & Advanced Sample Paper JEE Main Sample Paper-11

  • question_answer
    If\[\vec{a},\vec{b},\vec{c}\]are non-coplanar unit vector such that \[\vec{a}\times (\vec{b}\times \vec{c})=\frac{1}{\sqrt{2}}(\vec{b}+\vec{c})\]then the angle between the vectors\[\vec{a},\vec{b}\]is

    A)  \[3\pi /4\]                         

    B)  \[\pi /4\]

    C)  \[\pi /8\]                            

    D)  \[\pi /2\]

    Correct Answer: A

    Solution :

     \[(\hat{a}.\hat{c})\hat{b}-(\hat{a}.\hat{b})\hat{c}=\frac{1}{\sqrt{2}}\hat{b}+\frac{1}{\sqrt{2}}\hat{c}\] \[\therefore \]\[\hat{a}.\hat{c}=\frac{1}{\sqrt{2}}\]and\[\hat{a}.\hat{b}=-\frac{1}{\sqrt{2}}\] \[\Rightarrow \]angle between \[\hat{a}\]and \[\hat{c}=\frac{\pi }{4}\]and angle between \[\hat{a}\]and\[\hat{b}=\frac{3\pi }{4}\]


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