J & K CET Engineering J and K - CET Engineering Solved Paper-2008

  • question_answer
    If \[x\ne 0,\,\left| \begin{matrix}    x+1 & 2x+1 & 3x+1  \\    2x & 4x+3 & 6x+3  \\    4x+4 & 6x+4 & 8x+4  \\ \end{matrix} \right|=0,\] then \[x+1\]  is equal to

    A)  \[x\]           

    B)  \[0\]

    C)  \[2x\]            

    D)  \[3x\]

    Correct Answer: B

    Solution :

    Given,   \[\left| \begin{matrix}    x+1 & 2x+1 & 3x+1  \\    2x & 4x+3 & 6x+3  \\    4x+4 & 6x+4 & 8x+4  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[2\left| \begin{matrix}    0 & x & 2x  \\    2x & 4x+3 & 6x+3  \\    2x+2 & 3x+2 & 4x+2  \\ \end{matrix} \right|=0\] Applying \[({{R}_{1}}\to 2{{R}_{1}}-{{R}_{3}})\] \[\Rightarrow \] \[2\left| \begin{matrix}    0 & x & 0  \\    2x & 4x+3 & -2x-3  \\    2x+2 & 3x+2 & 4x+2  \\ \end{matrix} \right|=0\] Applying \[({{C}_{3}}\to {{C}_{3}}-2{{C}_{2}})\] \[\Rightarrow \] \[-4\left| \begin{matrix}    0 & x & 0  \\    x & 4x+3 & 2x+3  \\    x+1 & 3x+2 & 2x+2  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[-4x[2{{x}^{2}}+2x-(2x+3)(x+1)]=0\] \[\Rightarrow \] \[-4x[2{{x}^{2}}+2x-(2{{x}^{2}}+5x+3)]=0\] \[\Rightarrow \] \[4x[3x+3]=0\] \[\Rightarrow \] \[x+1=0\] \[(\because \,\,x\ne 0\,\,given)\]


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