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

  • question_answer
    \[\int_{{}}^{{}}{\frac{x-2}{x(2\log x-x)}dx}=\]

    A)            \[\log (2\log x-x)+c\]

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

    C)            \[\log (x-2\log x)+c\]

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

    Correct Answer: B

    Solution :

                       \[\int_{{}}^{{}}{\frac{x-2}{x(2\log x-x)}\,dx=-\int_{{}}^{{}}{\frac{\left( \frac{2}{x}-1 \right)}{(2\log x-x)}\,dx}}\]            Now put \[(2\log x-x)=t\Rightarrow \left( \frac{2}{x}-1 \right)\,dx=dt,\] then it reduces to \[-\int_{{}}^{{}}{\frac{1}{t}\,dt=-\log t=-\log (2\log x-x)}\]                                                                  \[=\log \left( \frac{1}{2\log x-x} \right)+c\].


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