9th Class Mathematics Related to Competitive Exam Question Bank Logarithms

  • question_answer
    If \[\mathbf{lo}{{\mathbf{g}}_{3}}\mathbf{2}=\mathbf{x}\] then the value of \[\frac{\mathbf{lo}{{\mathbf{g}}_{10}}7\mathbf{2}}{\mathbf{lo}{{\mathbf{g}}_{10}}\mathbf{2}4}\] Is

    A)  \[\frac{1+x}{1-x}\]                  

    B)  \[\frac{2+3x}{1+3x}\]

    C)  \[\frac{2-3x}{2+3x}\]               

    D)  \[\frac{3x+1}{3x+2}\]

    Correct Answer: B

    Solution :

    (b):Given, \[{{\log }_{3}}2=x\] \[\frac{{{\log }_{10}}72}{{{\log }_{10}}24}=lo{{g}_{24}}72=lo{{g}_{24}}\left( 24\times 3 \right)\] \[=log24+lo{{g}_{24}}3=1+\frac{\log 3}{\log 24}\] \[=1+\frac{{{\log }_{3}}3}{{{\log }_{3}}24}\]  \[=1+\frac{{{\log }_{3}}3}{{{\log }_{3}}(3\times 8)}\] \[=1+\frac{1}{{{\log }_{3}}3+{{\log }_{3}}8}\] \[=1+\frac{1}{1+{{\log }_{3}}{{2}^{3}}}\] \[=1+\frac{1}{1+3{{\log }_{3}}2}\] \[=\frac{1+3{{\log }_{3}}2+1}{1+3{{\log }_{3}}2}=\frac{2+3x}{1+3x}\]


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