CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    If\[\overrightarrow{x}=\overrightarrow{a}+\overrightarrow{b},\overrightarrow{y}=\overrightarrow{a}-\overrightarrow{b},|\overrightarrow{a}|=2,|\overrightarrow{b}|=3\]and the angle between\[\overrightarrow{a}\]and\[\overrightarrow{b}\]is\[\frac{\pi }{3}\],then\[|\overrightarrow{x}\times \overrightarrow{y}|\]is equal to

    A)  \[5\sqrt{3}\]                                     

    B)  6

    C)  \[4\sqrt{3}\]                     

    D)         9

    E)  \[6\sqrt{3}\]

    Correct Answer: E

    Solution :

    \[|\overrightarrow{x}\times \overrightarrow{y}|=|(\overrightarrow{a}+\overrightarrow{b})\times (\overrightarrow{a}-\overrightarrow{b})|\] \[=|-\overrightarrow{a}\times \overrightarrow{b}+\overrightarrow{b}\times \overrightarrow{a}|\] \[=2|\overrightarrow{a}\times \overrightarrow{b}|\] \[=2|\overrightarrow{a}||\overrightarrow{b}|\sin \frac{\pi }{3}\] \[=2\times 2\times 3\times \frac{\sqrt{3}}{2}\] \[=6\sqrt{3}\]   


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