JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{4}^{x}}-{{9}^{x}}}{x({{4}^{x}}+{{9}^{x}})}=\] [EAMCET 2002]

    A)                 \[\log \left( \frac{2}{3} \right)\]           

    B)                 \[\frac{1}{2}\log \left( \frac{3}{2} \right)\]

    C)                 \[\frac{1}{2}\log \left( \frac{2}{3} \right)\]

    D)                 \[\log \,\left( \frac{3}{2} \right)\]

    Correct Answer: A

    Solution :

                       \[y=\underset{x\to 0}{\mathop{\lim }}\,\frac{{{4}^{x}}-{{9}^{x}}}{x({{4}^{x}}+{{9}^{x}})}\],       \[\left( \frac{0}{0}\text{form} \right)\]            Using L-Hospital?s rule,            \[y=\underset{x\to 0}{\mathop{\lim }}\,\frac{{{4}^{x}}\log 4-{{9}^{x}}\log 9}{({{4}^{x}}+{{9}^{x}})+x({{4}^{x}}\log 4+{{9}^{x}}\log 9)}\]                                 Þ \[y=\frac{\log 4-\log 9}{2}\] Þ \[y=\frac{\log {{\left( \frac{2}{3} \right)}^{2}}}{2}=\log \frac{2}{3}\].


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