JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration of Rational Function by Using Partial Fractions

  • question_answer
    \[\int_{{}}^{{}}{\frac{1}{x-{{x}^{3}}}\ dx=}\]         [MP PET 1996]

    A)                 \[\frac{1}{2}\log \frac{(1-{{x}^{2}})}{{{x}^{2}}}+c\]

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

    C)                 \[\log x(1-{{x}^{2}})+c\]

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

    Correct Answer: D

    Solution :

                       \[\int_{{}}^{{}}{\frac{1}{x-{{x}^{3}}}\,dx=\int_{{}}^{{}}{\frac{1}{x(1+x)(1-x)}\,dx}}\]                    \[=\frac{1}{2}\int_{{}}^{{}}{\left( \frac{2}{x}-\frac{1}{1+x}+\frac{1}{1-x} \right)\,dx}\]                 \[=\frac{1}{2}[2\log x-\log (1+x)-\log (1-x)]=\frac{1}{2}\log \frac{{{x}^{2}}}{(1-{{x}^{2}})}+c\].


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