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

  • question_answer
    \[\int_{{}}^{{}}{\frac{1}{({{x}^{2}}+{{a}^{2}})({{x}^{2}}+{{b}^{2}})}dx=}\]

    A)                 \[\frac{1}{({{a}^{2}}-{{b}^{2}})}\left[ \frac{1}{b}{{\tan }^{-1}}\left( \frac{x}{b} \right)-\frac{1}{a}{{\tan }^{-1}}\left( \frac{x}{a} \right) \right]+c\]

    B)                 \[\frac{1}{({{b}^{2}}-{{a}^{2}})}\left[ \frac{1}{b}{{\tan }^{-1}}\left( \frac{x}{b} \right)-\frac{1}{a}{{\tan }^{-1}}\left( \frac{x}{a} \right) \right]+c\]

    C)                 \[\frac{1}{b}{{\tan }^{-1}}\left( \frac{x}{b} \right)-\frac{1}{a}{{\tan }^{-1}}\left( \frac{x}{a} \right)+c\]

    D)                 \[\frac{1}{a}{{\tan }^{-1}}\left( \frac{x}{a} \right)-\frac{1}{b}{{\tan }^{-1}}\left( \frac{x}{b} \right)+c\]

    Correct Answer: A

    Solution :

                       \[\int_{{}}^{{}}{\frac{1}{({{x}^{2}}+{{b}^{2}})({{x}^{2}}+{{a}^{2}})}}\,dx\]                                 \[=\frac{1}{{{a}^{2}}-{{b}^{2}}}\int_{{}}^{{}}{\left[ \frac{1}{{{x}^{2}}+{{b}^{2}}}-\frac{1}{{{x}^{2}}+{{a}^{2}}} \right]}\,dx\]                                 \[=\frac{1}{({{a}^{2}}-{{b}^{2}})}\left[ \frac{1}{b}{{\tan }^{-1}}\left( \frac{x}{b} \right)-\frac{1}{a}{{\tan }^{-1}}\left( \frac{x}{a} \right) \right]+c\].                 Note : Students should remember this question as a formula.


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