9th Class Mathematics Related to Competitive Exam Question Bank Logarithms

  • question_answer
    Find the value of x which satisfies the relation\[lo{{g}_{10}}2+lo{{g}_{10}}(\mathbf{4x}+1)=\mathbf{lo}{{\mathbf{g}}_{10}}(\mathbf{x}+1)+1\]

    A)  4                                

    B)  \[-4\]

    C)  1/4                              

    D)  not defined

    Correct Answer: B

    Solution :

    (b): \[lo{{g}_{10}}2+lo{{g}_{10}}\left( 4x+1 \right)=lo{{g}_{10}}\left( x+1 \right)+1\] \[\Leftrightarrow lo{{g}_{10}}2+lo{{g}_{10}}\left( 4x+1 \right)=lo{{g}_{10}}\left( x+1 \right)+lo{{g}_{10}}10\] \[\Leftrightarrow lo{{g}_{10}}\left[ 2\left( 4x+1 \right) \right]=lo{{g}_{10}}\left[ 10\left( x+1 \right) \right]\] \[\Leftrightarrow 2\left( 4x+1 \right)=10\left( x+1 \right)\] \[\Leftrightarrow 10x+2=8x+10\] \[\Leftrightarrow 2x=-8\Leftrightarrow x=-4\] When it is putting \[x=-4\]than \[log(x+1)\]) is not defined


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