JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{x{{.2}^{x}}-x}{1-\cos x}=\]    [IIT 1980; BIT Ranchi 1983; RPET 2001]

    A)                 0

    B)                 \[\log 4\]

    C)                 \[\log 2\]

    D)                 None of these

    Correct Answer: B

    Solution :

                       \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{x.({{2}^{x}}-1)}{1-\cos x}=\underset{x\to 0}{\mathop{\lim }}\,\frac{{{2}^{x}}-1}{x}.\frac{{{x}^{2}}}{1-\cos x}\]                                 \[=\log \,\,2\,.\underset{x\to 0}{\mathop{\lim }}\,\,\,\frac{{{x}^{2}}}{2\,\,{{\sin }^{2}}\frac{x}{2}}=(\log \,\,2)\,.\,2=2\log 2=\log 4\].


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