JEE Main & Advanced Mathematics Differentiation Question Bank Self Evaluation Test - Limits and Derivatives

  • question_answer
    Evaluate \[\underset{x\to \infty }{\mathop{\lim }}\,{{2}^{x-1}}\tan \left( \frac{a}{{{2}^{x}}} \right).\]

    A) \[a\]

    B) \[2a\]

    C) \[\frac{a}{2}\]

    D) \[4a\]

    Correct Answer: C

    Solution :

    [c] We have \[\underset{x\to \infty }{\mathop{\lim }}\,{{2}^{x-1}}\tan \left( \frac{a}{{{2}^{x}}} \right)=\underset{x\to \infty }{\mathop{\lim }}\,\frac{a}{2}\frac{\tan \left( \frac{a}{{{2}^{x}}} \right)}{\left( \frac{a}{{{2}^{x}}} \right)}\left( \frac{0}{0}form \right)\] \[=\frac{a}{2}\underset{y\to 0}{\mathop{\lim }}\,\frac{\tan y}{y}=\frac{a}{2}\]   \[\left( where\,\,y=\frac{a}{{{2}^{x}}} \right)\]


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