JEE Main & Advanced Mathematics Differentiation Question Bank Mock Test - Limits and Derivatives

  • question_answer
    The value of \[\underset{x\to 2}{\mathop{\lim }}\,\frac{\sqrt{1+\sqrt{2+x}}-\sqrt{3}}{x-2}\] is

    A) \[\frac{1}{8\sqrt{3}}\]  

    B) \[\frac{1}{4\sqrt{3}}\]

    C) 0                    

    D) None of these

    Correct Answer: A

    Solution :

    [a] \[\underset{x\to 2}{\mathop{\lim }}\,\frac{\sqrt{1+\sqrt{2+x}}-\sqrt{3}}{x-2}\] \[=\underset{x\to 2}{\mathop{\lim }}\,\frac{1+\sqrt{2+x}-3}{\left( \sqrt{1+\sqrt{2+x}}+\sqrt{3} \right)(x-2)}\]            (Rationalizing) \[=\underset{x\to 2}{\mathop{\lim }}\,\frac{\sqrt{2+x}-2}{\left( \sqrt{1+\sqrt{2+x}}+\sqrt{3} \right)(x-2)}\] \[=\underset{x\to 2}{\mathop{\lim }}\,\frac{(x-2)}{\left( \sqrt{1+\sqrt{2+x}}+\sqrt{3} \right)\left( \sqrt{2+x}+2 \right)(x-2)}\] (Rationalizing) \[=\frac{1}{(2\sqrt{3})4}=\frac{1}{8\sqrt{3}}\]


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