JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\tan x-\sin x}{{{x}^{3}}}=\] [IIT 1974; AI CBSE 1986, 90; AISSE 1983, 86, 90; RPET 2000]

    A)                 \[\frac{1}{2}\]

    B)                 \[-\frac{1}{2}\]

    C)                 \[\frac{2}{3}\]

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\tan x-\sin x}{{{x}^{3}}}=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\sin x-\sin x\,\cos x}{{{x}^{3}}\cos x}\]                 \[=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\sin x\,\left( 2\,\,{{\sin }^{2}}\frac{x}{2} \right)}{{{x}^{3}}\,\cos x}=\underset{x\to 0}{\mathop{\lim }}\,\,\left[ \frac{\sin x}{x}.\frac{2}{\cos x}.\frac{{{\sin }^{2}}\frac{x}{2}}{{{\left( \frac{x}{2} \right)}^{2}}}.\frac{1}{4} \right]=\frac{1}{2}\].


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