RAJASTHAN ­ PET Rajasthan PET Solved Paper-2007

  • question_answer
    If\[\vec{a},\text{ }\overrightarrow{b}\]and\[\overrightarrow{c}\]are non-coplanar vectors and\[\lambda \]is a real number, then \[[\lambda (\overrightarrow{a}+\overrightarrow{b}){{\lambda }^{2}}\overrightarrow{b}\,\lambda \,\overrightarrow{c}]=[\overrightarrow{a}\overrightarrow{b}+\overrightarrow{c}\overrightarrow{b}]\]for

    A)  only one value of \[\lambda \]

    B)  no value of \[\lambda \]

    C)  only three values of\[\lambda \]

    D)  only two values of\[\lambda \]

    Correct Answer: B

    Solution :

     (\[[\lambda (\overrightarrow{a}+\overrightarrow{b}){{\lambda }^{2}}\overrightarrow{b}\lambda \overrightarrow{c}]=[\overrightarrow{a}\overrightarrow{b}+\overrightarrow{c}\overrightarrow{b}]\] \[\Rightarrow \]\[\left| \begin{matrix}    \lambda ({{a}_{1}}+{{b}_{1}}) & \lambda ({{a}_{2}}+{{b}_{2}}) & \lambda ({{a}_{3}}+{{b}_{3}})  \\    {{\lambda }^{2}}{{b}_{1}} & {{\lambda }^{2}}{{b}_{2}} & {{\lambda }^{2}}{{b}_{3}}  \\    \lambda {{c}_{1}} & \lambda {{c}_{2}} & \lambda {{c}_{3}}  \\ \end{matrix} \right|\] \[=\left| \begin{matrix}    {{a}_{1}} & {{a}_{2}} & {{a}_{3}}  \\    {{b}_{1}}+{{c}_{1}} & {{b}_{2}}+{{c}_{2}} & {{b}_{3}}+{{c}_{3}}  \\    {{b}_{1}} & {{b}_{2}} & {{b}_{3}}  \\ \end{matrix} \right|\] \[\Rightarrow \]\[{{\lambda }^{4}}\left| \begin{matrix}    {{a}_{1}} & {{a}_{2}} & {{a}_{3}}  \\    {{b}_{1}} & {{b}_{2}} & {{b}_{3}}  \\    {{c}_{1}} & {{c}_{2}} & {{c}_{3}}  \\ \end{matrix} \right|=\left| \begin{matrix}    {{a}_{1}} & {{a}_{2}} & {{a}_{3}}  \\    {{b}_{1}} & {{b}_{2}} & {{b}_{3}}  \\    {{c}_{1}} & {{c}_{2}} & {{c}_{3}}  \\ \end{matrix} \right|\] \[\Rightarrow \] \[{{\lambda }^{4}}=-1\] \[\therefore \]There is no real value of\[\lambda \].


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