JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    The value of \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\sqrt{1-\cos {{x}^{2}}}}{1-\cos x}\]is

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

    B)                 \[2\]

    C)                 \[\sqrt{2}\]

    D)                 None of these

    Correct Answer: C

    Solution :

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


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