JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Determinats

  • question_answer
    Given \[a=x/(y-z),\]\[b=y/(z-x)\]and \[c=z/(x-y),\] where x, y and z are not all zero, Then the value of \[ab+bc+ca\]

    A) \[0\]

    B) \[1\]

    C) \[-1\]

    D) None of these

    Correct Answer: C

    Solution :

    [c] \[a=x/(y-z)\Rightarrow x-ay+az=0...(1)\] \[b=y/(z-x)\Rightarrow bx+y-bz=0...(2)\] \[c=z/(x-y)\Rightarrow -cx+cy+z=0...(3)\] As x, y, z are not all zero, the above system has a non-trivial solution so \[\Delta =\left| \begin{matrix}    1 & -a & a  \\    b & -1 & -b  \\    -c & c & 1  \\ \end{matrix} \right|\] \[\therefore 1+ab+bc+ca=0\]


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