CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2000

  • question_answer
    If\[\overrightarrow{a},\overrightarrow{b},\overrightarrow{c}\]are non-zero, non-coplanar vectors, then\[(\overrightarrow{c}\times \overrightarrow{a})\times (\overrightarrow{a}\times \overrightarrow{b})\]is:

    A)  parallel to \[\vec{a}\]

    B)  perpendicular to \[\vec{a}\]

    C)  parallel to the plane of \[\vec{b}\] and \[\vec{c}\]

    D)  perpendicular to \[\vec{c}\]

    E)  perpendicular to \[\vec{b}\]

    Correct Answer: A

    Solution :

    \[(\overrightarrow{c}\times \overrightarrow{a})\times (\overrightarrow{a}\times \overrightarrow{b})=[(\overrightarrow{c}\times \overrightarrow{a}).\overrightarrow{b}]\overrightarrow{a}\] \[-[(\overrightarrow{c}\times \overrightarrow{a}).\overrightarrow{a}]\overrightarrow{b}\] \[=\overrightarrow{a}[\overrightarrow{a}\,\overrightarrow{b}\,\overrightarrow{c}]-0=\overrightarrow{a}[\overrightarrow{a}\,\overrightarrow{b}\,\overrightarrow{c}]\] \[\therefore \]\[(\overrightarrow{c}\times \overrightarrow{a})\times (\overrightarrow{a}\times \overrightarrow{b})\]is parallel to\[\overrightarrow{a}\]


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