CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2006

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

    A)  \[\frac{\pi }{3}\]                             

    B)         \[\frac{\pi }{4}\]

    C)  \[\frac{\pi }{6}\]                             

    D)         \[\frac{\pi }{2}\]

    E)  \[\frac{\pi }{12}\]

    Correct Answer: C

    Solution :

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


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