RAJASTHAN ­ PET Rajasthan PET Solved Paper-2012

  • question_answer
    If a and b are unit vectors such that\[[a\,b\,a\times b]=\frac{1}{4},\]then angle between a and b is

    A)  \[\frac{\pi }{3}\]

    B)  \[\frac{\pi }{4}\]

    C)  \[\frac{\pi }{6}\]

    D)  \[\frac{\pi }{2}\]

    Correct Answer: C

    Solution :

    \[|a|=1,|b|=1,[a\,b\,a\times b]=\frac{1}{4}\] \[\Rightarrow \] \[(a\times b).(a\times b)=\frac{1}{4}\] \[\Rightarrow \] \[{{(|a||b|\sin \theta )}^{2}}=\frac{1}{4}\] \[\Rightarrow \] \[{{\sin }^{2}}\theta =\frac{1}{4}\] \[\Rightarrow \] \[\sin \theta =\frac{1}{2}\Rightarrow \theta =\frac{\pi }{6}\]


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