9th Class Mathematics Related to Competitive Exam Question Bank Logarithms

  • question_answer
    if \[lo{{g}_{5}}({{x}^{2}}+x)-lo{{g}_{10}}(x+1)=2\], then the value of x is:

    A)  5                                

    B)  10

    C)  25       

    D)  32

    Correct Answer: C

    Solution :

    (c): \[lo{{g}_{5}}({{x}^{2}}+x)-lo{{g}_{5}}\left( x+1 \right)=2\] \[\Rightarrow \,\,\,\,{{\log }_{5}}\left( \frac{{{x}^{2}}+x}{x+1} \right)=2\] \[\Rightarrow \,\,\,\,{{\log }_{5}}\left( \frac{x(x+1)}{x+1} \right)=2\] \[\Leftrightarrow lo{{g}_{5}}x=2\,\Leftrightarrow x={{5}^{2}}=25\]                              


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