JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{(1+x)}^{1/2}}-{{(1-x)}^{1/2}}}{x}=\] [Roorkee 1979; RPET 1996]

    A)                 0

    B)                 1/2

    C)                 1

    D)                 ?1

    Correct Answer: C

    Solution :

                       Multiply function by \[\frac{{{(1+x)}^{1/2}}+{{(1-x)}^{1/2}}}{{{(1+x)}^{1/2}}+{{(1-x)}^{1/2}}}\] and solve.            Aliter : Apply L-Hospital?s rule,                                 \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{(1+x)}^{1/2}}-{{(1-x)}^{1/2}}}{x}=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{1}{2\sqrt{1+x}}+\frac{1}{2\sqrt{1-x}}=1\].


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