JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
     \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{2}^{x}}-1}{{{(1+x)}^{1/2}}-1}=\]    [IIT 1983; Karnataka CET 1999]

    A)                 \[\log 2\]

    B)                 \[\log 4\]

    C)                 \[\log \sqrt{2}\]

    D)                 None of these

    Correct Answer: B

    Solution :

                       \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{2}^{x}}-1}{{{(1+x)}^{1/2}}-1}=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{2}^{x}}\log 2}{\tfrac{1}{2}\,{{(1+x)}^{-1/2}}}\]                                                 \[\left\{ \because \,\,\,\underset{x\to a}{\mathop{\lim }}\,\,\frac{f(x)}{g(x)}=\underset{x\to a}{\mathop{\lim }}\,\,\frac{{f}'(x)}{{g}'(x)} \right\}\]                 \[=2\,\log 2=\log 4.\]


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