JEE Main & Advanced Sample Paper JEE Main Sample Paper-20

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

    A) \[3\pi /4\]                          

    B) \[\pi /4\]

    C) \[\pi /8\]                                             

    D) \[\pi /2\]

    Correct Answer: A

    Solution :

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


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