CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2006

  • question_answer
    \[\int{\frac{dx}{x\sqrt{{{x}^{6}}-16}}}\] is equal; to :  

    A)  \[\frac{1}{3}{{\sec }^{-1}}\left( \frac{{{x}^{3}}}{4} \right)+c\]     

    B)  \[{{\cosh }^{-1}}\left( \frac{{{x}^{3}}}{4} \right)+c\]

    C)  \[\frac{1}{12}{{\sec }^{-1}}\left( \frac{{{x}^{3}}}{4} \right)+c\]   

    D)  \[{{\sec }^{-1}}\left( \frac{{{x}^{3}}}{4} \right)+c\]

    Correct Answer: C

    Solution :

    Let \[I=\int{\frac{dx}{x\sqrt{{{x}^{6}}-16}}}\] \[=\frac{1}{3}\int{\frac{3{{x}^{2}}}{{{x}^{3}}\sqrt{{{({{x}^{3}})}^{2}}-{{4}^{2}}}}}dx\] Put            \[{{x}^{3}}=t\] \[\Rightarrow \]               \[3{{x}^{2}}dx=dt\] \[\therefore \]  \[I=\frac{1}{3}\int{\frac{dt}{{{t}^{2}}-{{4}^{2}}}}\]                 \[=\frac{1}{3\times 4}{{\sec }^{-1}}\left( \frac{t}{4} \right)+c\]                 \[=\frac{1}{12}{{\sec }^{-1}}\left( \frac{{{x}^{3}}}{4} \right)+c\]


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