JEE Main & Advanced Sample Paper JEE Main Sample Paper-17

  • question_answer
    The value of \[\underset{x\to 1}{\mathop{\lim }}\,\frac{\sqrt[13]{x}-\sqrt[7]{x}}{\sqrt[5]{x}-\sqrt[3]{x}}\]is

    A)  \[\frac{44}{91}\]                                             

    B)  \[\frac{45}{91}\]

    C)  \[\frac{45}{89}\]                                             

    D)  \[\frac{45}{89}\]

    Correct Answer: B

    Solution :

     Let \[L=\underset{x\to 1}{\mathop{\lim }}\,\frac{{{x}^{\frac{1}{13}}}-{{x}^{\frac{1}{7}}}}{{{x}^{\frac{1}{5}}}-{{x}^{\frac{1}{3}}}}\]       \[\left( \frac{0}{0}\text{form} \right)\] Apply L? Hospital?s rule, we get \[L=\underset{x\to 1}{\mathop{\lim }}\,\frac{\frac{1}{13}{{x}^{-1+\frac{1}{13}}}-\frac{1}{7}{{x}^{-1+\frac{1}{7}}}}{\frac{1}{5}{{x}^{\frac{1}{5}-1}}-\frac{1}{3}{{x}^{\frac{1}{3}-1}}}\] \[L=\underset{x\to 1}{\mathop{\lim }}\,\frac{\frac{1}{13}-\frac{1}{7}}{\frac{1}{5}-\frac{1}{3}}=\frac{45}{91}\]


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