JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    If \[\underset{x\to 0}{\mathop{\lim }}\,\frac{[(a-n)\,nx-\tan x]\sin nx}{{{x}^{2}}}=0,\] where n is non zero real number, then a is equal to [IIT Screening 2003]

    A)                 0

    B)                 \[\frac{n+1}{n}\]

    C)                 n

    D)                 \[n+\frac{1}{n}\]

    Correct Answer: D

    Solution :

                       \[\underset{x\to 0}{\mathop{\lim }}\,n\frac{\sin nx}{nx}.\underset{x\to 0}{\mathop{\lim }}\,\left( (a-n)n-\frac{\tan x}{x} \right)=0\]                                 Þ \[n((a-n)n-1)=0\Rightarrow (a-n)n=1\Rightarrow a=n+\frac{1}{n}\].


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