JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2004

  • question_answer
        If    \[2a.b\times c\] and  \[a.b\times c\] \[a.b\] and \[3\hat{i}-2\hat{j}-\hat{k},2\hat{i}+3\hat{j}-4\hat{k},-\hat{i}+\hat{j}+2\hat{k}\] are non-coplanar vectors, then \[4\hat{i}+5\hat{j}+\lambda \hat{k}\]is equal to:

    A)  -1                                          

    B)  0

    C)  1                                            

    D)  4

    Correct Answer: A

    Solution :

                    since\[(1,a,{{a}^{2}})(1,b,{{b}^{2}})\]and\[(1,c,{{c}^{2}})\]are non-coplanar \[\therefore \]  \[\Delta =\left| \begin{matrix}    1 & a & {{a}^{2}}  \\    1 & b & {{b}^{2}}  \\    1 & c & {{c}^{2}}  \\ \end{matrix} \right|\ne 0\] and \[\left| \begin{matrix}    a & {{a}^{2}} & 1+{{a}^{3}}  \\    b & {{b}^{2}} & 1+{{b}^{3}}  \\    c & {{c}^{2}} & 1+{{c}^{3}}  \\ \end{matrix} \right|=\left| \begin{matrix}    a & {{a}^{2}} & 1  \\    b & {{b}^{2}} & 1  \\    c & {{c}^{2}} & 1  \\ \end{matrix} \right|\]                                                 \[+\left| \begin{matrix}    a & {{a}^{2}} & {{a}^{3}}  \\    b & {{b}^{2}} & {{b}^{3}}  \\    c & {{c}^{2}} & {{c}^{3}}  \\ \end{matrix} \right|=0\] \[\Rightarrow \]               \[\Delta +abc\Delta =0\] \[\Rightarrow \]               \[\Delta (abc+1)=0\] \[\Rightarrow \]               \[abc=-0\]                           \[(\because \Delta \ne 0)\]


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