JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{e}^{{{x}^{2}}}}-\cos x}{{{x}^{2}}}=\] [IIT Screening]

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

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

    C)                 1

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[x=\frac{1}{t},\]            Now expanding \[{{e}^{{{x}^{2}}}}\] and \[\cos x,\] we get            \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\frac{3{{x}^{2}}}{2\,!}+{{x}^{4}}\,\left( \frac{1}{2\,!}-\frac{1}{4\,!} \right)+.......}{{{x}^{2}}}=\frac{3}{2}\]            Aliter : Apply L-Hospital?s rule,                                 \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{2x{{e}^{{{x}^{2}}}}+\sin x}{2x}=\underset{x\to 0}{\mathop{\lim }}\,\,{{e}^{{{x}^{2}}}}+\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\sin x}{2x}=1+\frac{1}{2}=\frac{3}{2}.\]


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