JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    The value of \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{(1+x)}^{1/x}}-e+\frac{1}{2}ex}{{{x}^{2}}}\]is [DCE 2001]

    A)                 \[\frac{11e}{24}\]

    B)                 \[\frac{-11e}{24}\]

    C)                 \[\frac{e}{24}\]

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[{{(1+x)}^{1/x}}={{e}^{\frac{1}{x}\log \,(1+x)}}={{e}^{\frac{1}{x}\,\left( x-\frac{{{x}^{2}}}{2}+\frac{{{x}^{3}}}{3}\,-....... \right)}}\]            \[={{e}^{1-\frac{x}{2}+\frac{{{x}^{2}}}{3}\,-......}}=e\,{{e}^{-\,\frac{x}{2}+\frac{{{x}^{2}}}{3}\,-\,.....}}\]            \[=e\,\left[ 1+\left( -\frac{x}{2}+\frac{{{x}^{2}}}{3}-..... \right)+\frac{1}{2\,\,!}\,{{\left( -\frac{x}{2}+\frac{{{x}^{2}}}{3}\,-\,..... \right)}^{2}}+... \right]\]                    \[=e\,\left[ 1-\frac{x}{2}+\frac{11}{24}{{x}^{2}}-.... \right]\]                                 \[\therefore \,\,\,\underset{x\to 0}{\mathop{\lim }}\,\,\,\frac{{{(1+x)}^{1/x}}-e+\frac{ex}{2}}{{{x}^{2}}}=\frac{11e}{24}\].


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