CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    If\[\overrightarrow{a},\text{ }\overrightarrow{b},\text{ }\overrightarrow{c}\] are non-coplanar and \[(\overrightarrow{a}+\lambda \overrightarrow{b}).[(\overrightarrow{b}+3\overrightarrow{c})\times (\overrightarrow{c}\times 4\overrightarrow{a})]=0,\] then the value of\[\lambda \]is equal to

    A)  \[0\]                                    

    B)  \[\frac{1}{12}\]

    C)  \[\frac{5}{12}\]               

    D)         \[3\]

    E)  \[\frac{7}{12}\]

    Correct Answer: B

    Solution :

    Given, \[(\overrightarrow{a}+\lambda \overrightarrow{b}).[(\overrightarrow{b}+3\overrightarrow{c})\times (\overrightarrow{c}-4\overrightarrow{a})]=0\] \[\Rightarrow \]               \[(\overrightarrow{a}+\lambda \overrightarrow{b}).[\overrightarrow{b}\times \overrightarrow{c}-4\overrightarrow{b}\times \overrightarrow{a}-12\overrightarrow{c}\times \overrightarrow{a}]=0\] \[\Rightarrow \]               \[[\overrightarrow{a}\overrightarrow{b}\overrightarrow{c}]-0-0+0+0-12\lambda [\overrightarrow{b}\overrightarrow{c}a]=0\] \[\Rightarrow \]               \[[\overrightarrow{a}\overrightarrow{b}\overrightarrow{c}]=12\lambda [\overrightarrow{a}\,\overrightarrow{b}\,\overrightarrow{c}]\] \[\Rightarrow \]               \[\lambda =\frac{1}{12}\]


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