8th Class Mathematics Related to Competitive Exam Question Bank Logarithms

  • question_answer
    If \[\mathbf{x}=\mathbf{lo}{{\mathbf{g}}_{\mathbf{3}}}27\]and\[\mathbf{y}=\mathbf{lo}{{\mathbf{g}}_{9}}27\],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): \[~x=\text{lo}{{\text{g}}_{3}}27~~~~~y=\text{lo}{{\text{g}}_{9}}27\] \[\Rightarrow x=\text{lo}{{\text{g}}_{3}}{{3}^{3}}\,\,\,\,y=\text{lo}{{\text{g}}_{{{3}^{2}}}}{{3}^{3}}\] \[\Rightarrow x=3~~~~~~y=\frac{3}{2}\] \[\therefore \frac{1}{x}+\frac{1}{y}=\frac{1}{3}+\frac{1}{\left( \frac{3}{2} \right)}=\frac{1}{3}+\frac{2}{3}=1.\]


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