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

  • question_answer
    The value of \[\underset{m\to \infty }{\mathop{\lim }}\,{{\left( \cos \frac{x}{m} \right)}^{m}}\]is

    A) 1                     

    B) \[e\]

    C) \[{{e}^{-1}}\]            

    D) none of these

    Correct Answer: A

    Solution :

    [a] \[\underset{m\to \infty }{\mathop{\lim }}\,{{\left( \cos \frac{x}{m} \right)}^{m}}=\underset{m\to \infty }{\mathop{\lim }}\,{{\left[ 1-\left( 1-\cos \frac{x}{m} \right) \right]}^{m}}\] \[\underset{m\to \infty }{\mathop{\lim }}\,{{\left[ 1-2{{\sin }^{2}}\frac{x}{2m} \right]}^{m}}\] \[=\underset{{{e}^{m\to \infty }}}{\mathop{\lim }}\,\left( -2{{\sin }^{2}}\frac{x}{2m} \right)m=1\]


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