CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    Let a, b, c be distinct non-negative numbers. If the vector\[a\hat{i}+a\hat{j}+c\hat{k},\text{ }\hat{i}+\hat{k}\]and\[c\hat{i}+c\hat{j}+b\hat{k}\] lies in a plane, then c is

    A)  the GM of a and b

    B)  the AM of a and b

    C)  the HM of a and b

    D)  equal to zero

    E)  None of the above

    Correct Answer: A

    Solution :

    Since, vectors\[a\hat{i}+a\hat{j}+c\hat{k},\hat{i}+\hat{k}\]and\[c\hat{i}+c\hat{j}+b\hat{k}\] are   coplanar, therefore \[\left| \begin{matrix}    a & a & c  \\    1 & 0 & 1  \\    c & c & b  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[{{c}^{2}}=ab\] \[\Rightarrow \] c is the GM of a and b.


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