JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to \infty }{\mathop{\lim }}\,{{\left( \frac{x+2}{x+1} \right)}^{x+3}}\] is [MNR 1994]

    A)                 \[1\]

    B)                 \[e\]

    C)                 \[{{e}^{2}}\]

    D)                 \[{{e}^{3}}\]

    Correct Answer: B

    Solution :

                       Let \[A=\underset{x\to \infty }{\mathop{\lim }}\,\,{{\left( \frac{x+2}{x+1} \right)}^{x+3}}\]                       \[=\underset{x\to \infty }{\mathop{\lim }}\,\,{{\left( 1+\frac{1}{x+1} \right)}^{x+3}}\]\[=\underset{x\to \infty }{\mathop{\lim }}\,\,{{\left[ {{\left( 1+\frac{1}{x+1} \right)}^{x+1}} \right]}^{\frac{\,(x+3)}{(x+1)}}}=e\]                                                                                 \[\left\{ \because \,\,\underset{x\to \infty }{\mathop{\lim }}\,\,{{\left( 1+\frac{1}{x+1} \right)}^{x+1}}=e \right.\]                                            and \[\underset{x\to \infty }{\mathop{\lim }}\,\frac{\,(x+3)}{(x+1)}=\left. \underset{x\to \infty }{\mathop{\lim }}\,\frac{\,\left\{ 1+(3/x) \right\}}{\left\{ 1+(1/x) \right\}}=1 \right\}\].


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