JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    If \[x({{x}^{4}}+1)\varphi (x)=1,\] then \[\int_{1}^{2}{\varphi (x)\,dx=}\]              [SCRA 1986]

    A)                 \[\frac{1}{4}\log \frac{32}{17}\]

    B)                 \[\frac{1}{2}\log \frac{32}{17}\]

    C)                 \[\frac{1}{4}\log \frac{16}{17}\]

    D)                 None of these

    Correct Answer: A

    Solution :

               Here \[\varphi (x)=\frac{1}{x({{x}^{4}}+1)}=\frac{1}{x}-\frac{{{x}^{3}}}{{{x}^{4}}+1}\]                    Þ \[\int_{1}^{2}{\varphi (x)dx=\int_{1}^{2}{\,\left( \frac{1}{x}-\frac{{{x}^{3}}}{{{x}^{4}}+1} \right)}\,dx}\]                                                     \[=|\log x|_{1}^{2}-\left| \frac{1}{4}\log ({{x}^{2}}+1) \right|_{1}^{2}=\frac{1}{4}\log \frac{32}{17}\].


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