9th Class Mathematics Related to Competitive Exam Question Bank Logarithms

  • question_answer
    If \[\mathbf{x=lo}{{\mathbf{g}}_{\mathbf{3}}}\mathbf{27}\] and \[\mathbf{y=lo}{{\mathbf{g}}_{\mathbf{9}}}\mathbf{27}\] then \[\frac{\mathbf{1}}{\mathbf{x}}\mathbf{+}\frac{\mathbf{1}}{\mathbf{y}}\mathbf{=}\]______.

    A)  \[\frac{1}{3}\]                         

    B)  \[\frac{1}{9}\]              

    C)  3                                

    D)  1

    Correct Answer: D

    Solution :

    (d): \[x=lo{{g}_{3}}27\]        \[y=lo{{g}_{9}}27\] \[\Rightarrow x=lo{{g}_{3}}{{3}^{3}}\]\[y=lo{{g}_{{{3}^{2}}}}{{3}^{3}}\] \[\Rightarrow x=3~\]\[~y=\frac{3}{2}\] \[\therefore \frac{1}{x}+\frac{1}{y}=\frac{1}{3}+\frac{1}{\left( \frac{3}{2} \right)}=\frac{1}{3}+\frac{2}{3}=1.\]


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