JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration by Substitution

  • question_answer
    \[\int_{{}}^{{}}{\frac{\cos \text{ec}x}{\log \tan \frac{x}{2}}\ dx=}\]

    A)            \[\log \left( \log \tan \frac{x}{2} \right)+c\]

    B)            \[2\log \left( \log \tan \frac{x}{2} \right)+c\]

    C)            \[\frac{1}{2}\log \left( \log \tan \frac{x}{2} \right)+c\]

    D)            None of these

    Correct Answer: A

    Solution :

                       Put \[\log \tan \frac{x}{2}=t\Rightarrow \frac{1}{\tan \frac{x}{2}}.\frac{1}{2}{{\sec }^{2}}\frac{x}{2}\,dx=dt\]            \[\Rightarrow \text{cosec}\,x\,dx=dt,\] therefore            \[\int_{{}}^{{}}{\frac{\text{cosec}\,x}{\log \tan \frac{x}{2}}\,dx}=\int_{{}}^{{}}{\frac{1}{t}dt}=\log t+c=\log \left( \log \tan \frac{x}{2} \right)+c\].


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