JEE Main & Advanced Sample Paper JEE Main - Mock Test - 38

  • question_answer
    If \[x+y+z=0,4x+3-z=0\,\,and\,\,3x+5y+3z=0\] is system of equation, then which of the following is correct.

    A) It is inconsistent

    B) It has only single solution \[\operatorname{x}=0,\,\,y=0,z=0\]

    C) Determinant of coefficient of matrix is zero

    D) It has infinitely many solutions

    Correct Answer: B

    Solution :

    The given system of equations obviously has \[\operatorname{x} = 0,\,\,y= 0,\,\,z =0\] as a solution. Now, to check for the presence of non-trivial solution, \[\left| \begin{matrix}    1 & 1 & 1  \\    4 & 3 & -1  \\    3 & 5 & 3  \\ \end{matrix} \right|\] \[=\,\,1.\left\{ 9-5\left( -1 \right) \right\}-1\left\{ 4.3-\left( -1 \right).3 \right\}+1\left\{ 4.5-3.3 \right\}\] \[=14-1(15)+\left\{ 11 \right\}=10\ne 0\] Determinant of coefficient matrix is not zero. Since solution exists (unique) for the system of equations, it is not inconsistent. So, the system of equation has only single solution, \[x=0,\,\,y=0,\,\,z=0.\]


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